You don't understand casino accounting. Gaming WIN is revenue. If you put $100 in and get $75 out, that's $25 in marginal revenue with zero corresponding costs. The $100 is a statistic that the casino records, but it does not factor into profit calculations (total, or margin).

Gaming does have expenses -- labor (mostly dealers and slot attendants & mechanics), costs of purchasing and leasing the machines, and some other miscellaneous stuff... but profit margins on pure gaming are very high (and not limited in any way by the 25% maximum hold percentage that you reference)