You're probably not the first target audience for Google Maps widening their customer base, then, if you travel a lot across country borders in Europe. Most people move most of the time in their own areas without data roaming so this certainly will save them the cost of the license.

There's no real reason why Google couldn't solve that data roaming issue later, though, if it doesn't get solved by reasonable data fees by itself, by letting devices cache maps if they wanted to. There's been several news stories about Google making their own maps now in the USA and elsewhere, so they're not really (or won't be for long) tied to map licensing agreements either, I think that used to be the reason why the maps were "online only" (correct me if I'm wrong, I might be). So they might offer that option eventually, too.