Even discounting the exchanging of coins in person, what is your definition of "centralized"? Exchanges are independent from each other, and they pop in and out of existence as the wind blows. I would call them as centralized as email servers are.

Exactly, email servers like Gmail, Yahoo, hotmail are extremely centralized. Even if the protocol is open and anyone can technically speak on the same level, being big gives way more leverage over where the network is going.

Being centralized is not just being unique, it's being so powerful you get to decide your users' experience, instead of users being in control.