This is so all code is attributed to their correct respective authors, and shows the true power of open source -- not only do you get the current source, you also get the previous states, and all the information that carries with it.
You get to watch the process of Microsoft's code getting cleaned up and vetted. This is how it should be. This is how it must be -- think of our future digitally-inclined offspring, and how they will view 'history'. Shall it be an opaque black box of 'X happened.' or a transparent 'Here's thirty layers of wiki-depth, choose your interest level.' history? I prefer the latter. And http://simple.wikipedia.org/wiki/Category:Computer_science is a good start, and addictive! Help it grow!
Celebrate it. Let it be known, Microsoft is changing, just like IBM and Intel did after understanding and embracing linux and open source.
Community can make a difference. Let's show them how much, and welcome them to *our* community. They're beginning to listen. Let's not disappoint them.