Look at raid bosses in WoW. How often they move form their tanking spot (I know in GW2 there will be no tanks and bla bla)? Usually they just stand like log in the middle of chamber/lair so ppl can spread around and do their stuff, an nobody cares why Saurfang is not cleaving whole raid with single slash. If they just ran around and destroy everything around, because obviously they are almighty raid bosses, they would be unkillable.
Even better argument: bigass dragon is not going to follow single tiny dot somewhere in distance. If it throws some silly magic balls on him, he can just sent his minions, or deep breath on him and everyone around to kill him, if there's a big danger (Asura canon let's say) set a big defensive wall or fly up in the air. That's exactly what we saw in presentation at gamescom :P
So to be honest, I feel like GW2 bosses, where holy trinity is no factor, are way more realistic encounters than WoW raids.
P.S. I was a raider for over 3 years in semi hardcore guild and left that game immediatly when I saw GW2 dynamic events
