Indeed, in my experience dealers never pay the Ante bonus, as they are supposed to, when the dealer wins. I’ve seen this happen several times, and every time I had to summon the floor supervisor to get paid. To answer your question, the 2009 Gaming Revenue Report says that Nevada casinos earned $134,181,000 from Thee Card Poker in 2009. The house edge in Three Card Poker is 3.37% on the Ante and 7.28% on the Pairplus.
Let's assume the player bets both equally, for an average house edge of 5.325%. Dividing the profit by the house edge gives us the handle (total amount bet) of $2,519,830,986. Again, let's assume half of that, or $1,259,915,493, was bet on the Ante.
I roughly estimate the Ante bonus error costs the player 0.00072 of his Ante bet, on average, assuming the dealer always makes that error. So, over $1.259 billion bet, the cost of that error would be about $909,000 per year. However, to be fair, I'll say 25% of time the dealer won’t make that mistake, lowering that figure to about $682,000 per year. While that is a small fraction of the total amount bet in Three Card Poker, it is still not an insignificant amount of money. Hopefully this will educate players about this frequent error. Don't be afraid to throw the challenge flag if it happens to you or another player.
This question was raised and discussed in the forum of my companion site Wizard of Vegas.