Yeah lets be honest, UWP wasn't the greatest thing ever (although I can see the logic in the concept) but at the same time people like Sweeney (and EA etc) will moan as ultimately it could/would have hit his bottom line.
One thing for certain, Sweeney will always complain if it's something that ultimately could hurt his ambitions of being the main 'game store'... not that I disagree with all his complaints mind.
Sweeney will obviously like this change by MS because it helps in their fight with Apple etc to get the 30% fee reduced (I think it's too high and shouldn't be 30% on subs), as I said earlier it's ultimately about the money.