A good while ago I bought a 82cm Widescreen 100hz TV just because Gran Turismo 3 looked (looks) so great on it. Of course it's great for TV and movies also, but then I watched my movies on my PS2, so there.
I will buy a PS3 and then I expect at some point some stuff will look so much better in HD that I'll get a HDtv for it also (or computer screen). Being able to use a new TV screen for HD browsing as well as download and watch HD movies is certainly going to help make that choice for a HD tv easier. Especially the browsing is probably going to stimulate getting 1080p, as that resolution seems to match the way I use a TV pretty well.
You can't fully compare VHS with DVD. Just as there are big technological advantages that helped acceptance, DVD was also read-only, which didn't help. And lots of people had VHS tapes, which they couldn't play on their DVD player, so that didn't stimulate getting DVD either. Initially, DVD wasn't up against VHS, but against video-cd (in Europe and Japan) and Laserdisc (in the U.S.). Certainly it was that way in our stores in Europe - you had a slowly growing video-cd section (not nearly as big a success as it was in Japan) that was slowly but steadily taken over by DVD. Only when DVD burners became more popular did DVD start to push out VHS completely.
With BluRay, that's different. You can get a BluRay player and be future proof without having to sacrifice your current DVD collection. I had a nice little VHS collection and a lot of those movies I still enjoy, but I sold them off for practically nothing because my VHS player broke down and VHS tapes age badly anyway (not to mention the sound isn't quite up there). My DVDs though I'll be able to keep watching, and they'll probably look even better on a BluRay player, with upscaling abilities to all sorts of Progressive Scan stuff. Don't forget that many who have DVDs now don't have progressive scan capable TVs yet, so if they had a basic DVD player, they may actually be able to look at their DVDs in higher quality than they could before.
And that is apart from being able to get stuff like Lord of the Rings, the Pixar stuff, Star Wars and what-not in full HD resolutions, now, or in the future.
All that, mind you, quite apart from that I'd get the PS3 for the games anyway.