Well, I think there are a couple of factors:

* Racial skills - WotF has been mentioned and for good reason. It's a great way to avoid being fear-bombed. It's also no coincidence that some of the more popular multibox class setups can all be undead. (1xPriest, 4xLocks works... Mages can be undead, Warriors can be undead, etc)

* Physical size - 5xTauren can be an imposing force on the battlefield, and round-robin casting of War Stomp has potential, but you are also AN INCREDIBLY LARGE AND OBVIOUS TARGET. For a lot of players, especially mousing-controller folks, it's hard to resist targeting Taurens first. Also of note is that navigating Taurens through buildings, instances, tight spaces, etc can be a real bitch.

* Orcs - Orcs are compact, have a decent racial, and are allowed to be Shaman (a very popular multibox class at the moment). I personally rolled 3 more Orcs because my first shaman (their eventual teammate) happened to be an Orc. Were I to do it without that constraint, I might have rolled 4 Trolls because they are super sexy and have a nice casting animation. Alternatively, I think a Tauren main and 3-4 Orc followers could be nice for PvP, since you might be able to hide the orcs behind the Tauren to some degree.

* Draeni - Great racial skill for extra healing, even if their totems look awful.


Orcs FTW!!1!11