Also, what is the real difference between Centipede and Millipede?
This is based on what I read in books, and from what I've seen myself. I'm not sure if I'll make myself clear, either

With Centipede, you can develop a strategy to win the game. I've seen a guy (back when Centipede was still hot at the arcades) who used to get all of the mushrooms built up with a tunnel, and the centipede would come down the tunnel, and he would shoot it quickly. If you look at old "how to win" type books, you'll see authors who use this strategy.
With Millipede, there is a random regeneration of the mushrooms, and therefore there is no way to use these type of strategies. It's basically a vertical shooter where the 'pedes come faster and faster.
I find Millipede more fun since there's more variety. But for those who like to memorize Ms. Pac-Man levels, Centipede may be the better game.
Mario