No doubt they want to cache in on the metro apps and they will promote it. But their big cache cow is Office and the Server division. If they would restrict themselves to Windows 8 and Metro, they would cut off their own feet. That is not going to happen. How the enterprises are going to react to the metro UI is a complete unknown. By the time they will make up their minds, Windows 9 will be there and the process will start again. There are still an awful lot of legacy applcations which these companies are running (and which other users do not want to lose) and prevents MS to limit or remove the desktop in anyway.

 

And there is another thing: Microsoft already has done the certification track a couple of times - sometimes succesful, sometimes not (remember the logoo programs?). That never has been a restriction on which apps could be sold. At that time it was costly as well (in at least one of those programs you had to pay for the certification process).

The real question is why would you want to be in the store? Better exposure, better marketing, potentially more customers. So it is attractive to be in there. That is what Microsoft is gambling on. But this is in no way going to interfere with their much more profitable business

A bit OOT: In the early 80s Microsoft demonstrated the first demo version of Windows to us (pre version 1). Guess what it had? It was a tileable window environment with live content (although a complete different look, we'te talking about CGA video). In the released version, the live tiles went away, but still it is almost back to the beginning.