Right exactly, but in order to "play" with them, you need to be on the "same data center and the same server within that Data center"
Um, no. This is false. You are not locked to any one data center. You can choose to play on any server, located within any data center, at any time (you'll have to make a character for each of course)

People don't seem to understand what a data center actually is.

A data center is just a secure facility that houses server equipment. It's not some kind of impenetrable barrier that locks you into your region.