"an app store where MS thought they'd be able get a chunk of the piles of billions of dollars"
They seem to be making progress in doing that. MS recently announced they have had 3 billion visits to the store since Windows 10 was released. Also of note - Windows 10 customers are generating four and a half times more revenue per device than Windows 8 users.
Full blurb here: https://blogs.windows.com/buildingapps/2016/02/04/windows-store-trends-february-2016/