"Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game. Once a game has been made public, nothing in the copyright law prevents others from developing another game based on similar principles. Copyright protects only the particular manner of an author’s expression in literary, artistic, or musical form."

http://www.copyright.gov/fls/fl108.html

Anyone can sue you for any reason. It doesn't mean that they can win. But if they have money and they can pay fancy lawyers, they will probably find some technicality to take you out and rob you poor in the process. Live with it.

Not that anyone cares about his business practices but this guy only cares about money. His business doesn't bring wealth or prosperity to anyone other than him. What he's done in the past is shady and what he does now is probably worse. If you make a tetris clone, expect to receive a letter from his lawyers. And the letter demands that not only do you cease and desist your services (apparently it violates his rights), but demand that you pay royalties for each time your game has been played. What's even worse is that his company makes and produces games that take content directly from free online tetris games and then use his own games as leverage that the free tetris clones are infringing on his company (so make up a new tetris mechanic... he will steal it and then sue your ass off). I've done the research (and I'm far too lazy to post all of it, nor do I think anyone really cares enough to care). This guy has sent out hundreds of letters and lawsuits to people who have created or hosted free tetris clones online. Unfortunately no one in the field of making a tetris clone has the money to hire fancy lawyers to stand in court and that leaves some people with millions in debt to his company (so if your 16 and you made one for fun, don't post it online or distribute it). Props to him though, he actually practices what he preaches and not many people do that.