Casino's are just doing that to attract more gamblers, why not they try to show the losing stats of their gamblers.
I guess that will make other gamblers upset to show their lose, but showing up the profit of gamblers to their stats, that's encouraging people to gamble with them.
I think that is one of the strategy of a gambling site to attract more players. And almost of them display it for good. But does it really shows a legitimate stats without disguise?
Whatever strategy it is used in betting, you can't apply it in all kind of gambling. It might work in a particular game but not with the another.