Well, WoW is not nearly as latency-sensitive as online games like Counterstrike or probably IPX-based DOS games. It all depends on one basic question: "Can the program continue even if no answer from the remote side has arrived?".
Old network protocols often do excessive handshaking, which means they send some data and do nothing until the remote side has acknowledged the reception. That will kill performance on your link.
Modern ego shooters are likewise: In order to get an exact simulation and targetting behaviour, they do lots of round trips to make sure that they always know what the remote side knows.
In contrast to that, MMORPGs like WoW are designed from ground up so that latency is not as important. With thousands of players, there will always be some who have a bad link, either temporary or permanently, so the game was written to cope with that. Ever wondered why the combat procedure is different from "classic" multiplayer games? Those forced delays are one measure to reduce latency sensitivity. Did you notice how some people sometimes move jerkily, with sudden jumps in between? Same thing, clever programming to hide latency as good as possible.
TCP, the primary internet protocol, has also been designed with care. IPX-based software not, since people probably thought: "Oh, IPX only works on a LAN, latency is no issue"
So, to sum it up, chances are high that you can't do anything about it. But I hope you found the technical background information entertaining 😉