I expect BlackBerry apps would be first, since they still have the larger market share [1].

[1]: http://www.gartner.com/newsroom/id/2482816

The numbers are trending in MS's favor. Q12012 share for BB was 6.8 now only 3. Windows Phone in Q12012 was 1.9, now 2.9

Not rocket growth but the trend clearly points to MS being the weak #3.

Not sure how the existing install base for both effects this conclusion. Sales are only 1 piece of the puzzle.

For a vanishingly small market share? Not worth the effort. The web app works just fine.