Being able to produce the last 2 or 3 octaves with authority is why the good HT subs cost so much more. Much of the cost is in the driver. It doesn't cost much more to make an 18" driver versus a 12". The higher cost is in the development and production of the motor. Amps also have to be better, so costlier.
I'd bet you would also find that DJ subs are optimized for larger venues where critical listening doesn't exist and won't perform well in smaller rooms.