Rapid upgrade schedules are at least as much of a problem for both businesses and home users, as are Jurassic sized upgrades that only happen every three or four years.
For large businesses, an upgrade schedule of anything less than 2 years is likely to become an out of control disaster. My own company set a 5-year schedule, and with an employee roster of over 15,000 now, even that is a little aggressive. Add to that the rediculous hardware demands made by Vista, and subtract the fact that there really is nothing worthwhile to be gained from it in the business environment (Security and other manageability aspects are already being handled quite well by third party network-and-server-level vendors), and it's pretty clear that there is no value in yet another conversion.
For home users, As long as Microsoft can command obedience from hardware vendors like Dell and Compaq, every 'average joe' shopping for a new computer will simply 'live with' whatever came out of the box. They'd rather not have to think about it - and who can blame them? However, for people who already have a computer in their home, you guys are absolutely right - almost nodody I know, is going to look at their present Win2K or WinXP system, and say to themselves, "Gee whiz, I really need alpha levels.", and then go out and drop 2 or 3 grand on a new box. The headache of switching machines, for most folks, is just not worth the payoff.
So, I think this is one of the reasons why there's been so much 'bad blood' between the MS folks, and Dell, for example. Dell sees it's own fortunes being dragged to the bottom of the sea by the MS Vista Titanic, and they can't figure a good way out. That's also why I think *RIGHT NOW* would be a great time, to convince one of the hardware vendors to partner with a FUNCTIONAL linux distribution, and really push hard on the marketing. The Lindows/Linspire folks had the right idea, for sure, but just not the right time. The hardest part of making a plan like this succeed, though, is GAME VENDORS. Convincing them it'd be worth their while to invest time into producing Linux-compatible games would be a real chore, but without it, getting a biege-box linux system off the ground (or out of the store) would still be a struggle.