They are a total scam, because what you don't see, is the areas to the right and to the left of the surface, may not always be 'full' and therefore you don't really see how close the ones on the edge are to falling off. And, eventually, that will cause coins at the front (bottom of pic) to fall off the surface, and the player gets to keep those coins. You drop your coin in the back (towards the top of the pic) and once it is flat on the table, that ledge back there, pushes it foward, into the big mass of coins.
I can't explain it as easily as you can see it.
'Coin pushers' are these little mechanical type machines, where you take a quarter, drop it in the machine, it falls flat, and well, just click on this link. They monitor every coin that goes in every single machine.
Then they got made legal, and the proper term for them now is VLT (video lottery terminal) as they are all linked in with the State Lottery's headquarters in Charleston. Gray machines were the 'video poker' machines you mentioned, pre-2001(?).
