Actually, the reason why Microsoft and most software developers release beta's, rc's to specific groups is to help them do exactly what they are doing. To discover such issues which are missed in-house.
I think one of the problems is that since Microsoft is the most widely used OS on the planet the company lacks the true focus that you get when you trying to sell something. The people over at MS have become very slack in their jobs. They are too busy getting their hands into everything possible. I recently read where Microsoft and Ford Motor cars are joining up. Microsoft is trying to bump Sony's PS line with their XBOX. Microsoft is trying to bump Apple's itune & iPod with their Zune player. Microsoft is trying to outdo Google. I even read where Microsoft might be trying to develop their very own CPU.
Microsoft started out to be an Operating System developer, they should make that their priority over everything else until they get it right. Then again, MS Windows for the desktop never really was a marvel of technology. Everything they promised in their OS never really worked as they claimed, maybe not until their follow-up release. Which usually only fixed some issues.
With their hands in everything else it's no wonder they can't deliver on time or "innovate" anything new.
Everything the new Vista touts, is already in use in other OS's.