1.) People who don't know anything at all about random number generation, and just want a web form where they can press the button and get a random number.
You hardly need a hardware random number generator for this, or any kind of serious randomness.
2.) Acting as a neutral, trusted third party, for contests, etc. Dooce just did a big Microsoft-sponsored Kinect giveaway PR circus bullshit event, and they used random.org to pick the winners.
Unlike 1, there might be actual money in this, and is one of the few, amusing, businesses where the more money you charge, the higher the perceived utility.
3.) Providing random numbers as an advertisement for your fine line of hardware random number generators. Here it doesn't matter how much money you make, you just want people to buy the hardware that made them. Oddly enough, none of the random number services (and there are quite a few) do this, for some inexplicable reason. There's not even an argument-from-proprietary technology, since HRNGs are supposed to generate perfectly random noise, and there's no way an attacker could stage a replay attack.