Oh I know, it's just something that I like seeing when it (infrequently) happens.
I do have a hunch it'll be a bit more frequent in times to come; I think Blizz's storytelling ambitions mean that we're now at a stage where when they add a new zone, they want to carefully corral players within it to at least some extent.
Besides, it's much easier to balance open-world content if players can't drop in on the crucial areas from above!