Two points on this thread:
1. Casino's expect a 3-5% return collectively on all vp. This precludes the need to monitor an individual's skill level. Machines that habitually deliver a lower than expected handle are removed.
2. Casinos do monitor the specific machines being played. While they are hesitant to remove all positive machines, they are not hesitant to raise point requirements. Nor are they secretive about it. Fiesta went out of their way to let players know that they'd be earning points at half the normal rate by playing positive games.
I think that in many cases, people are anxious to assign some nefarious schemes to the casinos. Other than winning most of the money that you bet, there aren't any. The casino always has the edge over the pool of players, and they grow their edge by reducing benefits, not by fiddling with computer chips.
lb
"variance giveth, variance taketh away"