Guild Wars 2 - World vs World Gameplay Video
Three servers vie for control of a pvp island.
That's really a key part of Guild Wars pvp gameplay though... even with Guild Wars 1, finding spots where you could "sneak" into a battle from the edges and not be readily noticed right away by the people you're attacking was a big way to shift the odds of a battle - since its harder for your opponents to realize they're at a numbers disadvantage until it is too late.
Otherwise opponents just run if they're outnumbered. So basically, there have always been situations like that and they help keep the action going.