They simply needed a better compiler infrastructure to make Xcode and other tools smarter. You can see some good results of that in Xcode4.
They saw a great opportunity in an open source project (LLVM) and jumped on it.
No, I can't. It's proprietary and probably won't ever be ported to my platforms. This kind of crap is why I don't contribute to BSDL projects unless I'm being well paid.