Ha ha. I seriously doubt my group would be down for such a thing. Not exactly how we envisioned our youtube debut, and all that jazz.

But yeah, damage is a big part of it, and another part would be the players chat amongst themselves when it's not their turn, figuring out their next plan. Another part would be the fact that I generally stick to within 2 levels of the PCs' level (which means the PCs usually hit on about 7+ for the most part), and the huge damage output of the big three Blargney already listed - along with the fact that the leader can seriously add to the damage output and hit percentage of the group. (The Paladin, by the way, is also very useful in a sort of controller-y defender-y sense, though his marking is kind of pointless).
Quite often, the defenders will trade marks - the fighter will mark them all on one round, and the paladin the next. Also, the group has quite a few powers that let them make saves, so they're seldom out of the fight for long (the paladin has some "make a save" powers, and the bard made sure to take one or two as well, although he's much more focused upon moving his party members).
Also, and I think this might be a big part of it - the group will use dailies. Nobody holds onto them - at least one daily seems to be used every fight, and in the big fights, the dailies get dropped right at the start which can dramatically speed the fight up (the bard's "+5 Attack, +5 Damage on all allies' attacks" is basically a "we win this encounter" power, and the paladin's "+5 damage on all attacks until end of encounter" is probably better).
I have to say, the group is a pretty well-oiled machine at this point. Which works well for me - I can throw much larger fights than you'd expect at these guys, and they will often tear right through the fight.