During my time at Web 2.0 conference someone had brought up the lack of a Microsoft store for its products. I had the same thought a while ago but was corrected by one of my colleagues that we in fact do have a store that is just poorly advertised.
http://www.windowsmarketplace.com/
Unfortunately I totally forgot the URL and actually had a real hard time trying to find this link until today. I found it thanks to a Microsoft blog that talks mostly about our free software offerings but also mentions the store.
Free Software List
As I looked at this post I was actually surprised on just how much free software we give away. I know about most of it but there is nothing like having it visualized.
http://blogs.technet.com/blogms/pages/microsoft-free-software.aspx
Check out this link above and I think you will also be surprised in a good way.