I would say it is a little short sighted to say the reset occured because of .net. 

It was more a dependacy issue than a .net issue.  And a moving dependacy issue, things broke build to build because the underlying dependacy changed build to build. 

Add to that the Sasser, Blaster and other worm attacks and the obvious fact that updates were not being applied. 

Looking back, the Reset was caused more precisely by the Blaster Worm attack which forced MS to basically significantly rewrite and recompile portions of XP. portions of which were in 2k3. That undertaking took significant Manpower from the OS group to the support group at MS. Effectly stopping development on Vista.

The aftermath was that when sp2 was complete, the resulting code base synced with the 2k3 code base. And a Strong advancement in security from the base started in earnest. Part of the Security review was the new check in policy which was to ensure that the module was working before checked into main.  so the concept was scaled back.  also due to populiar demand some of the features were then abstracted and brought down level.  (avalon being the biggest one) 

of course this IMHO>

Douglas