Xbox Live Arcade games and Windows 8

So I bought Fruit Ninja Kinect (Xbox 360) a while back because my kids love pretending to be ninjas and chopping fruit on our TV. Then, I upgraded to Windows 8 and find that Fruit Ninja is available in the Windows 8 app store, but it will cost me $5 to get it.

If Microsoft really wants to one app store to rule them all, why should I have to re-buy Fruit Ninja to play on a difference Microsoft device? Shouldn't it already be unlocked? Is this Microsoft's fault? Is this up to the publishers in a way similar to the universal apps on the iOS app store?

I am sure that Microsoft has addressed this at some point, but I can't seem to find any information on it. Does anybody know if/when this is going to be fixed?