These are for reducing the effective cabinet size. Usually these pipes will be outside but will be hidden behind some other cabinets. Probably to make it look like a real monster they have made it like that.
these are ported subs and in ported subs, there is no requirement for the port to be inside the box. most people do it inside as otherwise it will look ugly, but you can have it outside also, that reduces the requirements on the box size also.
check out the hsu sub with turbocharger, its just the same thing. the port is extended to get a lower tuning frequency.