shadowfox
Anime Junkie
And from what I've seen they will be able to recreate it.
Tank - Warrior (MAYBE Guardian)
Heal - Water Ele / Guardian (MAYBE NECRO)
DPS - Thief / Fire Ele (MAYBE Necro)
Well, there's something to be said for that, but keep in mind that no matter what game you play, the dude with the armour is going to be responsible for containing the aggro in one place so the other's can nuke the hell out of it.
But besides that, every class has healing skills. Even the Warrior and Guardian. Ele's will be able to switch their affinities on the fly, so they can combine DPS and healing - I'm very sure the Necro is going to have some healing abilities as well. From what I see the Thief is also going to have a healing spec. And you forgot the ranger - DPS possibilities there if I've ever seen them.
I'm thinking people are going to go with what's comfy for them in the beginning, so I don't expect to see Ele's taking up all the aggro, but I DO expect to see them in the thick of things. The Guardian at this point looks very much like a support class - it's almost like a chanter/sorc combo in Aion in terms of buffs and crowd control.
I don't think we need to set things in stone just yet; Guildwars 2 is likely to bring a lot of unique implementations and combinations to the gameplay in general, much the same way that Guildwars itself did. I've tanked with both a Monk and Elementalist in Guildwars - I've used my Dervish and Ritualist to be main healers for a group as well. The possibilities are really endless.
Besides which, if you see too many bastards being elitist pricks (every game has them, so it's guaranteed) - hang with mates who you know like experimenting and don't mind a group wiping from time to time - all in the spirit of exploration and stuff like that. That's my MO anyways.