Should Google Open Up the Play Store to Other Platforms?

**Edit: Apparently I wasn't paying attention enough. Google already has Books and Music for iOS at least. :D

Obviously I'm not talking about Android apps. I mean for the music, books, and movies. This is what Amazon has done. Despite having a Kindle, they make their contents accessible on all the other platforms. Obviously the polar opposite are the others, including Apple and Google. Now we know Apple wants everybody to come into their walled garden. But Google? Wouldn't it be better if Google open things up so their contents can be accessed on other platforms as well as Android?

You would say Amazon does it because that's how they make money, while Google makes money form ads. Well, wouldn't it be better for Google to collect data about people's interest and patterns by allowing people with other platforms to have access as well?

Just a thought.