Casinos are designed for a single purpose: to separate you from your money. And they're good at it. Commercial casinos in the U.S. made nearly $35 billion in revenue last year, up a percent from 2009.
While they represent just a fraction of that revenue, slot machines are the casino gateway drug for the least savvy gamblers. It's why they're by the door. More than any other casino game, slots condition people to keep playing through positive reinforcement (bells and whistles). And the odds have gotten worse as technology has improved.
Though today's sophisticated multi-line machines have a higher "win-rate," the amount won is negligible, and often less than what was originally gambled. A recent study by researchers at the University of Waterloo in Ontario, finds that these multi-line machines are more effective than their single-line predecessors at taking money from the gambler by disguising losses as wins.