Gmail and Yahoo Mail and Facebook Mail and my personal mail server all stand in contradiction to your claim.
Stop making things up just because you want to complain about the Google. Nobody will fault you for a simple "Fuck Google, they're demonstrably evil and have access to way too much data now," which is what it seems to me you're driving toward.
Email is decentralized because Gmail, Yahoo Mail, Hotmail and whatever server you can setup can talk together. You don't have to use Gmail to send an email to a Gmail user.
The only thing that's threatening email decentralization is the war on spam. It's becoming more and more difficult to send messages that don't go directly to spam boxes if you're not one of the big player.
Stop making things up just because you want to complain about the Google. Nobody will fault you for a simple "Fuck Google, they're demonstrably evil and have access to way too much data now," which is what it seems to me you're driving toward.