I had heard about this already. AFAICR it had something to do with a lawsuit. But of course, Microsoft wouldn't mention that on their website. Also notice that the purpose of the drivers is to "enhance the performance of the Linux operating system when virtualized on Windows Server [...]". It's self-serving (not that Apple's contributions come out of the goodness of Steve Jobs' heart). Maybe I'm just too biased against big companies...
Well, I don't contribute to open source projects out of the goodness of my own heart either. I contribute because I use the software and gain a personal benefit from the contribution, you can't blame Microsoft for doing the same.