You dont have to tip them you know.
But for me, if I sit down with $100 and get up with $1000....thats $900 MORE than i came in with, had a good time, enjoyed myself and will thank the Dealer by leaving him $50-75. The more i win, the more i leave.
It was money I didnt have prior to coming in and had no intention of having when I left. So for me, its free money. Why not tip the guy who was in the right place at right time?