Fortunately, the official forums have provided me with a solution. Temari of Kil'jaeden wrote a simple Applescript which sets your Exposé hotkeys back to their default settings. Run it after you quit WoW, and everything is once more as it should be. Here's the application version of it; if you want to tinker or investigate, here's the source code [edit: links fixed]. The script's creator suggests adding it to your dock next to WoW. I don't use the dock much (Quicksilver forever, baby), but that's probably a good idea for those of you who do. By the way, this is apparently an Apple bug, so don't blame the blue.
Edit: Please stop posting your platform war comments. Whether they're pro-Mac or anti-Mac, I don't care; don't post them please. I don't want to have to start deleting people.