Everyone on this thread has to realize that they're effectively rebooting with Windows Phone 8 later this year again.[1] Maybe not to the degree of WinMo -> WP7, but it's certainly another disruptive (to the app devs) refresh.
As far as I know, they have yet to disclose the full developer story around WP8. We can certainly speculate, but I doubt they'll do anything too disruptive or they'll risk losing the small amount of market they've worked so hard to gain.
[1]http://www.winsupersite.com/article/networking/time-running-...