Who is surprised?
Linux is not a desktop OS. Linux apps suck to hell.
I use Linux since ever as a development platform. It works fine. Email and websurfing is ok too (thanks mozilla). But as soon as you have to write something or create and edit an image, linux software is pure crap. Compare gimp to Photoshop, open office to M$ Office or Pages? Surely you are joking, Mr. (put your name here ;o).
Linux is a hacker os made by hackers for hackers. Sometimes my impression is, kernel hackers don't have the slightest idea, what average computer users want and need. Thats why linux is marginal and will be.
There is no evidence presented that backs up the claim that Linux is being displaced by Apple usage; even stated is that in the time monitored Linux web users doubled (albeit to a still minute fraction of the total users). The assumption that having no Apple on the marketplace would leave a niche easily filled by Linux is also unlikely.
Apple is making good inroads in adoption, after a few costly moves reducing its market share, is gaining and hopefully continues to gain, traction and position itself as the consumer alternative to the nightmare of Windows. Linux is many different things, but the gain of community supported, easy to install, open source software will likely continue making inroads into the proprietary world. It remains to be seen if Linux can bridge enough proprietary apps to address the needs of Joe user.
In many of these systems, an important factor is the software ecosystem surrounding the OS itself: Windows has had this major boost and resistance to competition based on its 1-2 orders of magnitude greater availability of software than any of its competitors, but OS X is attracting a number of niche apps with major strong appeal to some user factions, and Linux is finally getting easy to use methods to access the plethora of good apps that make an OS stick.
That analogy only holds if increased OSX adoption is somehow inherently detrimental to Linux users. I don't see them competing with each other directly that much, as right now both OS are gaining primarily through Windows converts. The vast majority of hackers and power users aren't going to drop Linux completely for OSX, they'll just double boot or VM, and having a more Unix-centric focus in mainstream computing can only help to promote Linux software development.
I think Linux is now actually the OS that is the most easy to use, but it has only been a few weeks yet (release of Gutsy Gibbon) since the major issues have been resolved.
If you ask any random linux admin a question, the reply will be "You use that crappy version from last week? Install the latest version, THAT is the one that does it right."
This doesn't seem surprising in the least given that Apple spends tons of money trying to make people switch and I'm sure most Linux developers couldn't care less if windows users switch.
I assume this money you're referring to is marketing money.
If so, that's not what made me switch. I switched to a MacBook because 1) Suspend/resume would work reliably, 2) I would be able to plug in an external monitor and have it work without having to restart X and 3) I would be able to easily attach to WiFi networks, especially those using modern encryption.
Having supported hardware is a huge plus on laptops.
So I still use Linux on my desktop and I prefer X window managers to the Finder or whatever OSX's window manager is called. I also think that Linux package management is vastly superior to the mismash of package management options available on OSX.
Macs have always had more "killer" desktop applications (i.e. applications so compelling they drive the purchase of the underlying computer hardware) than random Linux boxes.
Apple created and dominated the desktop publishing area for a decade before there was such a thing as Linux. I know plenty of places full of Windows PC's that bought Macs to run PageMaker.
Apple's use of Postscript in their popular LaserWriter made a market for Adobe same way IBM's use of DOS made a market for Microsoft.
For more recent examples, I'd look to graphics and multimedia editing applications (e.g. Avid, Final Cut Pro, Photoshop, etc).
Would be interesting to know if Apple is gaining grounds in businesses or for private use. Most things you mention seem to be strictly for professional use. It's too bad that there is no Photoshop for Linux, but if people wouldn't pirate Photoshop, I doubt it would be as common as it seems to be now. Gimp does just fine for private use, though.
Most businesses I know might give a Mac to their designers, but the rest of the pack has to live with PCs.
Also, since you mention those "old" killer apps, apparently they were not killer apps enough to gain the Mac a significant marketshare a few years ago. So I question their deadliness.
As a counter-example, I have watched the entire "command-line or death" development group at my company move from linux desktops and laptops to macbook pros over the past year. Linux desktops still survive, but as peripheral machines under desks that are not being replaced when they die or the hardware becomes too slow. The only people clinging to PCs are sales and marketing people who live and die in Outlook.
As others have mentioned, the killer app for the Mac at the moment is being a unix box that "just works" and lets people get back to coding.
I use Linux since ever as a development platform. It works fine. Email and websurfing is ok too (thanks mozilla). But as soon as you have to write something or create and edit an image, linux software is pure crap. Compare gimp to Photoshop, open office to M$ Office or Pages? Surely you are joking, Mr. (put your name here ;o).
Linux is a hacker os made by hackers for hackers. Sometimes my impression is, kernel hackers don't have the slightest idea, what average computer users want and need. Thats why linux is marginal and will be.