Catalin Zima
No, I do not work for Microsoft.
The reasons they do not insist all entries to work on both windows and xbox 360 are, of course, hidden to me.
But if I were to guess, here's what I'd say:
The DBP is supposed to be a global competition. By enforcing xbox, all contestants would need a way to build for the xbox. That further implies: living in a country where there are xbox-es (this is the restriction in my case), having one, and having a Creator's Club subscription. Since they want as many original and innovative ideas as possible, it seems only logical that they would want to allow those of us who don't have the above mentioned requirements to participate.
However, since the winning game of the main phase will probably be published to XBLA, if that game happens to be one made for Windows, they are probably just making sure the transition to xbox will be smooth, by requiring the use of GSE.
That's my view on the subject.