I love GW2, but really, this is something no one knows yet. Maybe all high level Dungeons rely on simple hit&run gameplay, maybe the only "tactic" you'll have to know is "run away when the boss charges"or "everyone punch that guy" and stuff like that.
WoW's raid bosses seem to be one of the few things everyone cheers about (didn't play it myself for that long, cause I got bored fast), so yeah. I'd say we'll wait until someone actually has seen high level dungeons before we defend them with our lives
I think it's very hard to create intriguing bosses with clever team-based tactics needed, if every character basically can do the same. I also think Anet can pull it off, but I'm not yet convinced.