i think that the whole 'trick' of powerlevelling is that that is all they do...
they dont stop to use the bathroom, or answer the phone/door, and they dont stop to get something to eat... they've got many people taking shifts so that the everyday calls of life (bathroom, etc.) wont interfere with your character's levelling
for instance, you would have to stop maybe every 2 hours or so to take a !@#$%^&*, or maybe get a bite to eat... or answer the phone, get the door, pick up a pizza... all this combined would perhaps take away a half hour of potential grinding... when people are powerlevelling you, there's no interference, it's just hardcore grinding with no breaks
also if you get up to use the phone, uh oh! a horde/alliance kills you while you were afk... there's 10-15 mins running back to your corpse and healing back up that could have been spent levelling
hope that helped
