It's an interesting thought for sure. However, it's just like a poker/casino site. The "rake" is generated by the fish. The site doesn't care if the top earners stay or go. It only cares about drawing in more fish.
Sit at a poker table with 9 other top earners and you are the fish......YOU pay the rake for the table. The casino only cares that there are a few of you at each table. The winners will be the winners, and if they leave someone else will step up and take their place.
You need recreational players that come back again and again for whatever reason. (Not a perfect analogy, but not bad.)
Any poker forum has the same ongoing debate. "You know they stack the deck to screw the winners and make them leave." Or, "you know they give the fish the 'miracle card' to keep them around." Bullsheeet.
Renni is also correct, but WGT doesn't intentionally gameplan to kick these guys out. They aren't employees with salaries, pensions, taxes, benefits, and many other actual liabilities incurred. And, if I had someone generating 75% of my sales, I'd be retarded to let them go if they were still profitable to me. I'm not going to find the same generation of revenue for less money, unless said employee is grossly over paid. But, that's a different debate for a different day.