The legacy servers aren't the old servers. SE changed up the server architecture for ARR, so the old servers wouldn't work anyway. the legacy servers are where all the characters transferred from 1.0 are. Right now, characters from 1.0 aren't allowed to be on the normal servers (though it is possible to create a new character on a legacy server, iirc). SE is planning to allow 1.0 characters to be transferred out of legacy servers in a few months. Otherwise, they're the same as the regular servers.