Well, Microsoft is at an impasse here: I work for a large Enterprise, and we of course use Windows almost exclusively, and perhaps this is not their target, yet I will say this: None of our apps are going through that store. They're all coming from direct from vendor purchases, of which Microsoft gets Zero.
under this model, it encourages (perhaps) some of the smaller/medium Enterprise vendors to give up having to deal with a payment system at all, in exchange for simplified distribution (if I read this correctly) and no more payment handling, and in exchange MS gets a 5% cut.
This to me makes complete sense. Most of the Windows ecosystem for software is mostly out side of Microsoft's hands. Indeed, it is the #1 strength of the platform beside its ubiquity.
I actually think this is a brilliant insight on the side of Microsoft, by inverting this model they get a non-zero slice of a a pie they previously did not have.
It also encourages more vendors to uptake the distribution model via their Store, which I think is ultimately what they want more than a cut of sales in aggregate.
Say nothing of the home user, who beyond MS Office perhaps never transacts at all with Microsoft when they buy other software.