It would force Microsoft's application developers to play on the same field as any other developers. I think this makes far more sense than forcing Microsoft to auction off or give away the source code for Windows, which is another proposal making the rounds. In fact, this whole issue conjures an amazing sense of deja vu. Plus, some companies hide behind the banner of standards and openness while delivering something less. Most consumers don't care about source code one way or another, and wouldn't know what to do with it if they got it.
Most businesses have no use for the source, either.
I think the 'Free Windows' battle cry is a false issue, and that the open-source code issue is moot. Open-source code, no way. There's not much in that column I'd change, even a year later. But opening the APIs would avoid many of the drawbacks while providing much of the benefit.