If a casino did cheat, people would lose too quickly, and take their business elsewhere. Internet sports bettors also encounter a number of problems not found when betting with a regular sports book. Gee, thanks a lot.
Poker works differently, both in cyberspace and in real poker rooms.
The house doesn't play against the player. The House's only interest is having a full table, and the more full tables the better. I could envision it, if the operators were undercapitalized or faced losses from other business operations. In live poker games, players always have to be wary about players who pool their resources, in an effort to trap other players. Player A bets, B calls, C raises, A raises, and B folds, because he figures that his hand isn't strong enough to play against C, who has raised, and A, who has re-raised.