Roy, remember that scene in the first Alien movie (1979), where that little cute baby Xenomorph bursts out of the crew member's chest?
Well, 'Modern Apps' are exactly like that. They do NOT belong in Win32, they're completely alien to it.
What MS was/is trying to do is come up with a closed version of Windows (which, of course, is NOT Windows at all, just runs on top of - or inside - it for the time being) which they can have absolute control over so, among other things, developers are forced to sell their apps through the Windows store, which would render MS a 30% cut of *every* app ever sold without them having to do anything.
So, being alien to Windows, those 'modern apps' have alien DNA. You can't splice Human DNA with Alien DNA - just doesn't work. Two very different universes. 