First, despite the simplification of the cables, physically connecting it can still be a challenge, for example if there's no convenient place to put a laptop within 6' of the TV. And power for the laptop there too.
Second, once its connected, it's no certainty that the external display will be correctly detected or set to the correct resolution. Is the picture streched? When you hit full-screen, does it only show on the laptop? Is sound going over HDMI too? Tinkering with settings and troubleshooting a multi-monitor setup can be intimidating for the "average consumer".
Even if you get everything setup, many laptops do no come with remote controls, and long HDMI cables are uncommon.
I've owned or own a Roku, a TV which had USB and could play anything FFMPEG could read, a PS3 with netflix and recently an AppleTV+iPad.
I'd consider myself reasonably technically inclined and have had an HDMI cable which comfortably reached my couch for quite awhile but I still use that as a last resort for content I can't play some other way.
I do this too, but (as lazy as this might sound) I'm definitely much less inclined to watch TV knowing that I'll have to go through that process vs. grabbing the remote and pressing 'power' and flipping through the channels (which is perhaps a good thing as far as my health goes). It's annoying having to stand up to switch between things too.
I also have a Google TV with the Plex app, which is great except my laptops aren't quite fast enough to stream 1080p over wifi (and even 720p can sometimes have buffering problems too). Plex is pretty simple as far as these kinds of things go, but even with Plex I can absolutely imagine the average consumer having trouble, or just being too intimidated to even try to set it up ("I have to run a "server" on my computer? What the hell is that?")
Anyway, my basic point is that there's really nothing as smooth and simple, even for people like us who have no trouble setting up a media server, as it was in the "old days" where you can pick up the remote and be watching what you want to watch within 10 seconds.
There are loads of internet enabled TV's on the market at the moment that in the UK at least will give you access to youtube, lovefilm (similar to netflix), BBC iPlayer and the streaming services that most channels provide. Similarly the PS3 and XBOX can do similar things. The UI's probably need some work but IP-TV is becoming a reality.
It depends on what you are using as a UI, but probably. If it boots into a full screen, remote-controllable app that never crashes, then it might be ok.
I toyed around with Boxee for Mac on a dedicated old laptop and it was really close -- crashed too much, but if it didn't, it would be fine for a lot of consumers -- though not nearly as good as AppleTV. The advantage over AppleTV is the enormous amount of content.
