I think majority of the rude players are directly from WoW, and are from the group of gamers that expect instant gratification with no effort. These players are irritating for me also, I usually leave group if they bother me too much (trash talking is unacceptable for me imo).

I think WoW has ruined a lot of the MMO community by being so casual friendly and by making gear so easy to get. Players don't realise that games are suppose to be hard and they don't realise that everyone in the party is important to the group.