Actually, there's a fairly good reason neither Google nor Apple has really gotten into content creation hardcore: they are both businesses based primarily in content *distribution*. . . and reliant on other companies wanting to distribute their content through said services. Third parties would get *really* leery of selling their music through iTunes, for example, if they were competing against iSongs produced and recorded by iMusic. Apple would have a strong incentive to favor their own in-house products, and even if they didn't, nobody on the outside can tell for sure they *aren't*.
A rule of thumb in business: never compete against your own customers. It seldom ends well. The only exception I can think of is Steam, which avoids the problem largely by Valve having largely abandoned the video game publishing business.