It's a research project, not an actual product MS wants to sell. So how is this different from the dozens or hundreds of bleeding-edge experiments that demand a current version of Chrome/FF to work and refuse to do anything on any other browser?
As I said in my comment, it's not how Microsoft have done things, ever. IE10 isn't even shipping as a final product for the most widely deployed version of Windows, and Windows 8 has basically no market share.
The difference with Mozilla and Google is I don't need to migrate my entire OS to use their experimental stuff.
