I personally believe all pure chance gambling should be illegal, but since like poker this is a game of skill where you interpret the actions of others it is a little less problematic.
If only pure chance games were illegal, would people just add some teensy unimportant skill element to otherwise pure chance games?
By law competition organisers used to have to do this here so that it didn't compete with state run lotteries. They usually required you to answer a question in addition to submitting your tokens/coupons/whatever. One state used to have a law which stated that you couldn't require a purchase in order for someone to enter a competition so people from that state got one free entry.