I imagine they have servers at different locations. Probably close to population centers. The main game office is located in LA so that's why it's all PST. Distributing your servers across geography is one of the few tried and tested ways of reducing latency.
For those not in the know, latency is the amount of time it takes your signal to travel to the server. If the server is not close to you geographically, it may add seconds to your response time. MMO's have never had one server in one location connecting the entire world together. It's always been a mesh network distributed across the world.