Question : Why the hell don't Microsoft have an app-store?

I don't mean why they haven't built an entirely new distribution network for some projected new Windows mobile phone operating system. I mean, why didn't Windows 7 Desktop launch with a complete "give us your credit card number and we automatically install, manage, upgrade everything for you automatically" sort of thing?

I had managed applications from a central repository of packages on my Debian system in 2001. I have it seamlessly on Ubuntu (and have had for a good while). When Apple came along and showed the world that owning an app-store was a great business to be in, all the other mobile providers rushed in and started building their own.

What M$ could have done, is set a few engineers building something similar, for integration with Windows 7. I don't mean a website, I mean something more like win-get (or Debian's apt-get).

I'm installing software on my wife's new Windows 7 laptop today, and I'm amazed, now I come to think about it, that there's no "buy apps" option under the Windows Start button, right next to the list of already installed applications. Why is there no search-box built into Windows to let me find Microsoft-approved 3rd party applications to buy?

Think what a feature this could have been for Windows 7. How it would have driven corporates to upgrade (too expensive to pay our own IT people to install software, better to pay for the new Windows and let Microsoft sort it out.) How it would have energized the MicroISVs and lone developers to continue to invest their energy in Windows (rather than start dabbling on Android and iOS). How it would have given M$ a cut of all the software sold in the Windows eco-system.

The more I think about it, the more this seems like it would have been a good idea, and the more the absence of an app-store in Windows 7 seems like an extraordinary oversight. Was one planned but not finished in time? Was Microsoft too scared of potential legal implications to do with competition? Did they just slip up?