Unified Windows and Phone?

I've seen a lot in the press lately about how MSFT's long-term plan involves, amongst other things, a scenario where a consumer could simply purchase a single app that would scale itself to various form factors.

It's a wonderful concept, but I think the reality wouldn't be as neat. It's an approach that's certainly failed Google thus far. And from a consumer standpoint, I can see the potential for immense confusion around app functionality, especially since Windows will probably indefinitely retain some degree of focus on desktop use cases. Even if the underlying code is largely similar, I still think there is value in having separate apps for various device categories.

What I'd prefer to see is a much more sophisticated app store/model that would allow app "families" to be linked in a way that's obvious to consumers (I confess that I do like the idea of a unified store, if it's well organized), while still remaining separate.

I dunno, am I along in this line of thinking?