WoW has more worlds than that.
Kalimdor
Eastern Kingdoms
Northrend
Outland
I hear you though. What difference does it make anyways? Either you fly to another planet on one hand, or you travel through a funneled path on the other.
WoW certainly did have mountains that blocked your way until blizz negated them by adding flying mounts. WoW is as linear as you jumping from one stupid point to another.
Also, swimming out to 1.5 miles is inconsequential.