like the pun, andymac 🙂 sorry that I'm probably about to buzzkill it with a semi-serious answer, haha.
while my doctorate in phys ed hasn't shown up in the mail yet, I'm pretty sure this is going to fall back into one of those "depends on the person/intensity/etc." kind of answers. I'm totally on board with your theory because I imagine a lot of cardiac-intense things would provide a good workout and help shed some pounds.
in the end, I'm gonna agree with persona and go start advertising that for the gyms around here!