Just a Heads-Up on this OP.
I got a conflicting response about this from an on-line discussion with a MS rep, so I queried the Support Team and got this reply:
MS Rep says: The app has to be usable with keyboard and mouse input in any combination. (mouse or keyboard is acceptable) or the limitations have to be disclosed in the app description page.
So in other words mouse only is OK!
The problem was that the mouse wasn't working on their test machine as discussed in this thread.