It's perfectly possible to hold 4+ mobs as a warrior. The most important thing I have to do is get them arranged in front of me. After the initial threat application of Tclap, I have a few seconds to Devastate the couple mobs that didn't get Tclapped.
What messes me up mostly is someone pulling aggro, then I have to run to get it back, and the nice orderly setup degenerates into a frenzy of spamming threat on every target I can get my hands on and hoping that I don't miss one by chance.
"I played hard to avoid mistakes, but now I can play hard to capitalize on opportunities." -Arold, on the 3.0 Protection Warrior.