Not if you judge by my recent random heroics - AN on Solidfaith and Zul'Drak on Solidstar.
By the way the trigger for this post is an excellent post by PvD about what the Death Penalty really means. Go read it :)
However at the end PvD talks about how in WoW 5-man PuGs frequently kick a person who is under-performing or under-geared. Or easily leave group (especially if they are the tank) if they think they will save more time.
While this may be true in general, not all PuGs are like this. See Honor's Code PuG's Tale for a nice example of a good PuG.
Here are also 2 of my recent stories.
Solidfaith had a bumpy heroic AN start the other day, with a paladin tank who after the first 2 trash groups left the group without even a word. I can only assume he was upset at the DPS for pulling agro. Instead of everyone leaving group or myself leaving the group (which would have activated the 15 minuted debuff), we all stayed and chatted till and after less than 5 minutes (probably closer to 2 but I'm being cautious here) a new tank joined and we cleared the instance easily and without a wipe. Yes, the DPS were far from perfect, especially a noobish warrior. But there are many ways to deal with such issues and the most useless one is quitting the group without a word. Still the point is, the 3 DPS and myself didn't go into a fit when the tank left but waited the few minutes required to find another.
Solidstar had a much bumpier ride. Being an under-geared tank, it is hard for me sometimes to hold agro. Or for healers to keep me up. Well yesterday or was it the day before (only my RSS feed knows :p) I got into a heroic Zul'Drak random. Paladin healer, 3 DPSers. A few pulls later and it is obvious I'm going to have to work hard at keeping agro. But I like the challenge and the run goes relatively okay up until King Dred. At this point the rogue I think suggests we try the achievement. We try but I take too much damage from all the raptors hitting on me at the same time and die so we wipe. The healer rage-quits. Now at this point the DPS could have rage-quit as well, but they stay on and we get another healer. We go for the boss as you normally would, but the healer and a DPS die. I manage to stay alive long enough to the DPS to kill the boss, but as there is on one able to rez the healer and dead DPS, we are forced to wait. Again at this point any of the others - healer and DPS - could have rage-quit over the near wipe and long wait, but they don't. We continue on the groups in the next corridor, up the stairs and to the last few mobs before the last boss who are the annoying fearing DKs. Well at this point the DPS make an error and run in front of me and pull agro from the first 2 DK's + the patrolling single one. I might have been able to save even this from a wipe, but one of them gets feared into the back group of 2 DKs and pulls them as well. Wipe, and a DPS leaves. Now, I don't exactly blame him for leaving - it was annoying to wipe. But it was also stupid to leave at this point, with only 3 mobs between us and the final boss (we did manage to kill 2 adds). We quickly found another DPS, the dead people ran (well except for the rogue who didn't release and I could see the healer wasn't going to rez him but in the end one of the other DPS rezzed him) and we finished the instance. So sure, it wasn't pretty and it wasn't quick but the point is those players who stuck it out till the end prove not all WoW players look for the OP group to boost them through the instance.