Are Sony movies really that much of a selling point? I can't name any blockbusters from Sony.
Anyway what you said COULD work but they would need to wait until their install base for playstation certified tablets/phones are large enough. But if they continue to offer their music and movies on iTunes what would be the reason to buy a PS certified product? This is a tough decision.
I can see them dominating the games store though. You'll eventually be able to buy PSP games and play them on tablets/phones that are PS certified. Eventually Vita games will be available as well. This would be a huge selling point.







