I was kinda hoping windows7 would feature a completely redesigned os where nothing pre-vista would run
Not going to happen, period -- Microsoft's entire empire is build around lock-in.
If you can't run any of your old software, only two things can happen:
1) People will cling for dear life to the existing versions (even more so than people sticking with XP instead of switching to Vista)
2) People will use the opportinity to switch away from windows altogether. I mean, if none of your legacy applications will work and you have to start over fresh, why not switch to Linux or Apple that have at least some existing software market out there?
In a way, this is a bit what happened to Intel: It's 64-bit Itanium processors were technically much better than AMD's x64 extensions, but it was not backwards compatible with the x86 architecture, so people couldn't run their existing software on them.
Along came AMD with a technically 'worse' solution that did enable people to run their old stuff, and it pretty much sunk Intel's multi-
billion dollar investment completely. Not much later Intel silently adopted the x64 extensions as well, and here we are today, using yet another layer on top of an outdated CPU architecture.
(The x86 platform really is a horrible cludge -- it has scaled upwards pretty decently due to ever-increasing optimizations, speed increases and multi-cores, but at a low level it's a horrible solution. Compared to pretty much every other CPU architecture x86 is horrible to program for -- for example, you only have 4 CPU registers to store your variables, while even the old Motorola 68000 that the Atari and Amiga used had 16 of them)
Anyway, to get back to Microsoft: Don't underestimate how many people actively dislike them -- there is very little brand loyalty or mindshare towards microsoft. There are a lot of people and corporations that only stick with them because they pretty much have to at this point. If you take that reason away, all bets are off again.
Microsoft would NEVER give up it's market monopoly voluntarily, henc there's no way they would give up their existing backwards compatibility. It's both a burden and blessing for them.