What we've seen will continue: consoles have begun to merge with HTPC's in their ability to play digital music, movies, photos, etc. They can't record/play tv shows, but can stream them over their internet connection via some tightly controlled channels (hulu, netflix, etc.). Since the console controls the TV, I think this trend will continue. HTPC/Apple TV's don't stand a chance.
That said, there will always be a need for a standalone PC to do WORK on. You could use a spreadsheet in the living room, but you wouldn't WANT to (maybe with binoculars).
PS - For all those arguing a price difference, I think it's almost 0. If you think ahead and buy a regular sized case, you can swap out the video card every 2-3 years and play the latest games on your PC. Averaging the high cost of consoles over their 6 year life, gives you a couple midrange video card upgrades.