Casino "Cheating"

Some local people where arrested for allegedly "cheating" some casinos. Besides the bribing allegations and other insider dealings, I never really understood how this is considered cheating. Aren't they just using all the available information to improve their play; all the other players have access to this information as well. I remember reading about casinos banning card counters in blackjack. A lot of them weren't using any devices, just counting the cards in their heads. The casinos are free to let whomever they want play, but it goes to show just how much pull they have with politicians that they can make it a "crime" to get good at their games.