This is the single biggest thing that relegates them to "just a consumer electronics" firm - and as we know, CE firms are lucky to have 10 years on top.Yeah this is the thing exactly. Amazon and Google are essentially content plays in mobile. Devices can come and go but as long as people are using their services they're making money.
Apple is a hardware play and that gave them a big first-mover advantage but unless they can keep coming up with iPhone/iPad level home runs that advantage deteriorates quickly. I will never buy anything in iBooks, for example, because I don't want to be limited to Apple's devices to read my books, even if I do currently have an iPhone, iPad and MBA.
They do have some platform tie-in with iTunes Music but the writing is on the wall there. Subscription models are the way forward.