It would help if there were mobile games worth paying for.

The technology behind cell phones is improving, but the graphics are nowhere near on par with the PC cousins. However...the average cell phone can hold data and process games on par with PC games from 10 years ago.

I can think of plenty of PC games from 10 years ago I'd just love playing out on the road. Unfortunately, mobile developers tend to shy away from complex gameplay and cater to the lowest common denominator.

Modify Civilization 2 or 3 to work with a small touchscreen.
Modify Sim City 4 to work with a small touchscreen.
Modify Railroad Tycoon 1 or 2 to work with a small touchscreen.
Modify the earlier (complex) Final fantasies to work with a small touchscreen.

Regretably, the mobile versions of these games were not modifications or enhancements of the originals, but dumbed down "Farmville" equivelents.

I suppose I might consider mobile "Hearthstone" an exception. I bet it's not included in these figures, as purchasing card packs is generally done on the PC, then transfers over to the mobile version.