Some sites also use their online poker purely as a side line to win over traffic into their online casinos. On average they take 5% of every pot, or 5-10% from every tournament entry fee. That is called rake. Rake is also present in real Casinos.
There are no specific state laws that prohibit online poker operators from operating within the state. However, state authorities are extremely firm in their stance on illegal poker games or gambling in general they don't like it one bit.