What you use and how you use it has a lot of factors besides age. It has to do with your friends, their friends, where you live, what school you go to or what job you have, etc etc.
I'd like to share an anecdote about umwelt. A few days ago, I walked into a coffee shop. I sat in that coffee shop for two hours. When I first walked in my jaw hit the floor as I scanned the room. Everyone had tablets, young, old, there was no common pattern. There was one person I could see reading a physical book, and two graphic designers in the back with Macbooks. My first thought was "Either I'm living in a bubble, or coffee shops are a bubble.".
I figured that if this is what it looks like in suburbia, then it must be even crazier elsewhere. That's when it hit me. If silicon valley developers do their work in coffee shops, and all they ever see there is mobile devices, then they'll naturally develop for mobile devices. But then mobile is new, hot, and growing all the time. IIRC mobile sales have already outdone consumer desktop and laptop sales.
Are developers choosing mobile because it's new and big, or because they see it in coffee shops all the time? Probably both. They're not exactly mutually exclusive. Just like how you have to ask if consumers are switching to tablets because laptops are too bulky, or because they're more usable, or because that's where the focus of every up and coming developer is right now? Probably a combination of all three and more.
All of that might have seemed pretty obvious to you. Well it wasn't to me, heres why:
1. In my circle of friends, everyone still uses desktops or laptops. Having only a laptop seems to be a result of financial concerns, not a lack of demand for a desktop.
2. At my school a handful of people have tablets. Me being one of them. A group of kids asked me what kind of cellphone it was when I first used it in class.
3. Among my friends Facebook seems to be the dominant communication medium, alongside telephone services. I only use the latter.
4. My school has uncommon demographics, The vast vast majority could be described as one or more of the following: Nerd, Hipster, Extreme anime and manga fan, Gamer. So I guess I myself sort of live in a bubble. I don't even own a cellphone.
I live on the west coast of the US. Not exactly a remote location.
: This was the first time I've ever actually sat down in a coffee shop.
Subsequently, however, tablets seem to have almost completely disappeared from cafe/coffee-shops; usage on trains is also down. Maybe people still use them at home or something I dunno, but at least in public usage they showed every sign of a classic fad...
Interestingly, laptop usage doesn't seem to have recovered... most people either chat to real friends, use their smartphone (often together with their friends), ... or read (yes, real book usage seems to be up quite a bit)...
I wager it's just too annoying to carry around a tablet, and smartphones are now good enough that they've largely displaced them in public "on the go" usage, where portability is a key factor.
You have a lot of good thoughts about the mobile/tablet stuff and I think you're right. Just to add some quantitative info to it, I work for an e-commerce site and a quarter of our traffic is mobile, and that's not including people using our native mobile apps, which means that our real mobile traffic is more than 25%. I don't believe that includes tablets, but I'm not sure (there isn't a tablet-specific site, although we do have native tablet apps.)
Honestly, every time I use a tablet the first thing on my mind is the firmware invading my privacy. The next thing though is input devices. (I'll probably end up flashing cyanogen mod.)
Input devices, for most users, and even most developers, are something assumed. For desktop it's keyboard and mouse, for laptop it's keyboard and some kind of mouse-like input device. For tablets it's touch or buttons. For phones it's touch or buttons. (I don't think most tablets that use buttons, like e-readers, are open for development. Correct me if I'm wrong though.)
I'm going to reiterate what I've already said before, touch sucks as a universal interface.  So my question ends up being "What peripherals make sense for a mobile device?". Recently I received a tiny bluetooth keyboard to type on my Nexus 7. That's a step in the right direction, as typing things out with the on-screen keyboard is painful and awkward. (And since a stylus is too slow, smudges up the display...)
For a pointer device I am using a capacitive stylus. My current hypothesis is that the dominant paradigm for tablets will be keyboard and pen. Though for delicate tasks such as drawing, a capacitive stylus leaves much to be desired. IMO touch should be, in the majority of cases, a fallback interface for people without peripherals. For most applications it doesn't beat traditional input devices such as pens keyboards and mice of one sort or another.
Your complaint about touch interfaces probably has more to do with buying a really shitty MP3 player than anything inherent about touch.
I just mentioned I have a Nexus 7. Same complaints mostly. Though the touch is more responsive in the 7, doesn't really alleviate my complaints. (I never complained about latency on the Sanza because it's a sub $100 device and can't be expected to have decent capacitive touch hardware. Which is part of the reason it should use buttons, there was no reason to make it a device driven by touch.)
That and I haven't seen very many "gestures" in the android apps I use. Though I've heard a lot of hype about them.
>Touch beats pens, keyboards, and mice in the respect that you don't have to carry around a bunch of peripherals. Nearly everybody has fingers and spent the first couple years of their lives learning to use them.
Yes, yes it does. Which is why it was probably a smart idea to force developers to assume only a touch screen for most applications, it stops them from requiring a stylus for stuff that doesn't need it. At the same time, using a tablet with just your fingers is really painful, and theres no way I'm the only person who holds this opinion.
And theres a reason tablet keyboards are so small, and usually clamp onto the device they're built for, it's because nobody is going to lug around a full sized 104 key desktop keyboard. And pens are small, they fit in your pocket easily. Together they probably fix enough of the weaknesses touch has as an interface to make a tablet usable as more than a toy.
when I say touch should be a "fallback" interface, that might imply it shouldn't receive regular use. I really mean something closer to "default". A good example might be GIMP. (Or any other image editor, like photoshop.) People who are serious about drawing digitally usually buy a drawing tablet, or in decades past some sort of light pen. But because drawing tablets work like any other pointing device from the operating systems perspective, users who prefer a drawing tablet can use one without locking out users who only have an optical mouse, and vice versa.
A capacitive touch stylus is compatible with touch screens, meaning that for applications that don't require extreme delicacy, pens and touch can co-exist without carrying around any large peripherals. Users who don't want to buy any fancy add-ons are happy, users who can't stand smudging their screen and cleaning it with a glasses cloth are happy too.
That's the only way in which it beats those things, in particular keyboards. In most other aspects (e.g., usability) it falls far, far short.
Are developers choosing mobile because it's new and big, or because they see it in coffee shops all the time?