While the country is poised to re-consider current laws making online gaming illegal, online companies are pouring a lot of money into developing robots that can play poker. There are some games in which it's easy to build a bot that can win.
But in poker, an imperfect information game, there are many unknown variables. A player does not know his opponents' cards and may not know their style of play -- how aggressive they tend to be, for instance, or how often they bluff.
Unlike a chess bot, a poker bot does most of its work before the match, running millions of simulations before the first card is dealt. But even with the large amounts of memory available with today's computers, storing -- or even computing -- information for every possible scenario would be implausible.