You are missing the key difference between Google's Youtube app and Maps app. The key differentiating factor is that iOS 6's built-in Map app maybe sufficient for, let's say, 50% of the casual map users, whereas pretty much everyone who wants to use Youtube on iOS 6 has to have some sort of Youtube app. If Google were to make a paid Map app, that might cause some (or many) of other 50% users to continue using the build-in app for maps. So for the remaining 20-30% of the power users who would want to pay for a Google Maps app, I am not sure if it's worth the effort. Then again, all this might be incorrect and we might see Google Maps app in the coming days.