@devSpeed - Server apps (SQL Server) and individual apps (LightRoom, IE 9) are not on the same scale as a all of .net. A framework that supports thousands of apps.
Server apps because upgrading a single server is a far less difficult prospect that upgrading thousands of client machines. And the server is frequently under the control of the party that needs the upgrade. Client apps are frequently controlled by a third party and forcing an OS upgrade is far more difficult.
Individual apps are also different because there scope is smaller. Even IE that has a huge install base, does not have the wide reaching scope of that the .net framework has.
@ZippyV - It is the bugs I don't know about that bother me. Microsoft will not release a list of all the fixed bugs. So I have no idea what to look out for until it has bit me.
@felix9 - I have no idea what the chance of hitting one of these bugs is, because no one (unless you are a Microsoft insider) knows what the bugs are. But a good example is this one: If you have a collection that is grouped and sorted, then adding the first item can crash your app. Because I know about that one, it will not mess me up. But I have no idea how many more like that there are. And if I cannot see them while I am debugging then that adds $$$ to my development and/or introduces bugs to production.
@cbae - Security fixes are not what concern me here (though those are very important until April 2014). I am talking about .net framework bug fixes.