Who is to say there won't be a two tier situation when Nextbox comes out? I remember the NES continuing to have a significant following long after the Megadrive/Snes came out. Also the PS2 kept soldiering on under people's TVs, long after it should have been long gone.
I seem to remember VHS players still being sold a couple of years after DVD came out. There may be a significant number of people who say "this is good enough for me, for now".
I think it's Xbox Live that makes the difference here, there's a lot of people on there - many of whom are casual and not the types to adopt new technology quickly. As long as there are enough subscribers to XBL, why would Microsoft cease to support it?
I feel this gen may be slightly different from the earlier generations. Obsessive gamers, rich folks and graphic-whores will grab the Nextbox immediately, while another type of gamer (busy family men, retro gamers, casual gamers and skint folk) may well continue nattering on Xbox Live for another couple of years after Nextbox's release.
I can see 360s continuing to be manufactured and sold for a while longer than we are used to consoles surviving (I know they already have, but I mean even longer - even after the release of Nextbox)...
*awaits bitter, sneering sarcasm and analogies regarding things being dropped*
