Vegas doesn't make more money based on who wins. The house gets a set % on win-place-show bets and a different set percentage on exacta's, Tri's and super's. All of the rest of the money in the pool goes back to the players to be divided by the winning tickets. The more winning tickets there are the less the payout. The fewer number of winning tickets the higher the payout.
All the monies are paid out minus the set house commission. The Belmont was not fixed.