Eh? I claim it's the norn and probably true of all those airports. The pathway isn't always very prominently marked however. I've only personally done it at CPH and DUB (before the new terminal, I think it's harder to find now). It's also very obvious at YUL in the international wing.

Can you name any airport outside the uk which doesn't allow exiting the international departures area via immigration? It's an odd idea, people miss or cancel flights all the time.