My old hiking bag had a zipper fail last year and I called it bursting. You're totally right though, it just broke at the seam. That's actually a helpful way to look at it for fixing stuff.
Yeah, zipper teeth can get bent out of shape or the slider just wears out. I fixed mine by getting a heavy duty YKK slider from a fabric store and using pliers to clamp it on the old track. Works like new now.