wrong. there are a few heroic bosses that require everyone in the group to do a minimum of 10k dps.
best example: 3rd boss in shadowfang-keep.
well i can only speak for the classes i played myself, those being: dk, mage, paladin, rogue, druid, warrior.
all of them are able to do a minimum of 10k dps when they just reached ilvl329 (mostly with tricks like using some pvpgear in inventory and such)
including the tank-specs
(tanks only on total average. singletarget they do a bit less of course.)
also note, those 10k+ are NOT doable in any dps-spec in that gear. but everyone should respec anyways once you reached 85.
a few specs, like sub-rogue(unluckily those always suck in pve) and frost-mage(possible but only with lots of crits which is unlikely with 10-15% critchance) are simply too weak compared to their better heroic-specs (combat, fire).
with other words: i dont have a clue why it is okay for so many people to be a burden to the group ...