That sure would be one way to combat people who use it as a money laundering platform. I've seen much more stringent wager requirements than 25%. 
I don’t think it would be a very effective way of detecting money laundering (or attempting to do so). Someone who wanted to try to launder coin could simply repeatedly bet the minimum bet, having the maximum chances of winning each bet, then withdraw once they have bet 25% of their deposit.
A 25% wager requirement might cut down on the number of stupid people using their casino as a mixer and the number of requests from law enforcement asking about what happened to various deposits.
I personally think the OP is less concerned about the wager requirement and more about the confirmation requirement.