Updating and rebuilding Android

Really simple:
If the system lets you get away with having to do less changes to a package to get it working, then *of course* there are going to be fewer changes. People want to get stuff working, and make only the necessary changes.
Or are you really saying that build system and structure have *no* influence on the result? My experience says otherwise...

About making things public and involving kernel people: Yes, that would have helped for getting changes upstream, but it would not have helped to get the product out faster. The Kernel developer community is focusing on getting it done right, while their own development team has to focus on getting it done fast (or at all). Considering the amount of pressure on getting stuff to the market fast, there's only so much time you can spend on figuring out the right approach...

So how would getting things in patches have been far worse, if the patches themselves are under version control? Having patches under version control means that you have *at least* the same amount of information available that you have now, but with an extremely easy way of structuring things even more if you feel like it, which (using quilt) costs virtually no extra effort.