Assuming I'm reading this [1] right, the FSF seem to believe that Apple App Store (where the majority of mobile app profits are being made) isn't compatible with the GPL.
You don't, but as I pointed out this seems to be where the majority of app revenue still comes from. Cutting that out as an option makes it much more difficult to make much money from app development.
App stores are profitable for a small number of UX experts. It's very hard for me to imagine many open source apps having good enough UX to survive the app store hunger games.
