I have a suspicion that at some point Microsoft are going to back down on the big deal-breakers. They don't try to push their luck with those kinds of games in their enterprise products, because the big customers simply won't accept them. The frequent failures are just proving the critics right, and there have already been tentative moves to moderate the problems with mandatory updates. If changes in that sort of direction go far enough, they will appeal to smaller but serious customers who aren't running enterprise editions but have similar concerns.
If Microsoft really don't take the hint and back down when it comes to the crunch, I suspect Windows 7 will make the immortality of XP look like an amateurish trial run. I know my businesses all stocked up on Windows 7 machines a couple of years back while we still could, and since then we've been actively investigating multiple possible alternatives to Windows desktops for future use. Looking for alternatives seems to be the general trend across the other small tech businesses within my network as well, so if Microsoft think they're going to call everyone's bluff and get the whole world to migrate to 10 next year by shutting off updates for 7, I suspect they have seriously misjudged their market.
The actual deal breaker are bugs who can be exploited and need to be fixed. And while its unfair to expect bug free software, fixing them is not new functionality.