What these services fail to realize is that they're selling fungible digital commodities. You can sell them as a subscription model, but the one-for-one relationship between copy and user must be maintained. For this you need a registration system. And immobilization. And verification.
And then with the Digital Content Exchange, you have at least one method of making money off the whole process.
But without fixing the ecosystem, these models are going nowhere. Amazon sells other things, and can bankroll what must be losses in this area in exchange for extending its brand (it's cheaper than advertising). And oh by the way the book publishers and authors aren't happy either. Maybe there's something rotten in Denmark??