It's the players with a solo-role mentality, the ones who will refuse to adapt to circumstances and the ideals of GW2 that worry me.
The example I presented earlier is (I think) a valid one: A group of 5 go into a dungeon. One player won't lay traps, heal, debuff or assist other than by laying out ranged DPS. The other group members are forced to work around him, holding on to specific duties to compensate and cover his ass. The more often you're forced to deal with a particular mentality, the more likely you are to respond in the same manner over and over, until it becomes second nature. Before long, your plate wearer is always trying to be a tank, a scholar is trying to be the main healer, and DPS give up their tricks and alternate abilities just to get the dungeon over with.
Think of it like selfish behavior in LFD groups. Everyone rolls need 100% of the time, because if they don't, they'll lose a main spec piece of gear because some jerk will roll need for off-spec. You started off generous and considerate, now it's every man for himself; you've altered the way you do things because of the actions of others. (let's please not get into an argument over LFD etiquette
)
With a little luck, a group is destined to fail if everyone doesn't play their roles dynamically. If not, the "pure" spec players have an opportunity to push everyone else into a static role. We won't really know until NDA-free beta reviews come in.