VAK - I was coming up with a hypothetical, but guys who get a $3g payday which is intended to cover training often spend more training for the fight than they make from fighting. Saying its their business model doesn't excuse it.
I would imagine the UFC pays far less in overhead. Lorenzo almost says they pay $100g or so (up to $999,999 since its a 6 digit figure) for the arena. I figured they split that, and they usually get a gate of $2m or more. On most nights, the attendance covers salaries and venue costs.
As far as advertising goes, most of that is covered by the PPV providers. The UFC of course pays for temporary billboard space, but the ads you see on cable/satellite come out of the providers share of the revenue
Other sports pay the training costs of athletes, pay benefits (health, pensions), pay managers directly, pay guys who aren't actually playing. I would imagine the UFC pays a lot less than other sports, not more.