Re: Be afraid!
A large part of their hopes from an improved bottom line from Windows 10 will come from moving everyone to the new platform and being able to do away with support for the older platforms.
As for the store, I've not seen a single Windows Store app that is actually any good. Microsoft's own attempts are anywhere between half-arsed and just plain terrible. Build a first-class system that will make people want to use it because of how well it meets their needs and watch the users and the money roll in of their own accord. It's not that difficult to figure that one out.