maybe 75% of the people I know (which is anecdotal, i know, so its not good statistics) probably would give me a blank stare if I explained to them the difference between 480, 720, and 1080 i or p.
I agree with one of the above posters up there when he said that most people buy HDTV's because they're flat and their big. And anything that flat or big will be HDTV anyways.
As for the setup, I would argue that the "average" or at least "casual" gamer will probably set up their systems using composite cables, if not component cables. This of course, means that they will not be able to see the full 1080p-ness of a game, as it were. I'm sure that at least one person in the world has tried to hook up their PS3 using an RF adapter.
My point is perhaps the HD penetration rate might not be as good as an indicator as you think when it comes to PS3 or XBox sales.
That being said, I'm pretty certain that people will buy PS3 because of its better graphics, even though some people will have it set up all wrong anyways. I hope it makes sense :-p