In a boxing game users can throw punches or duck, and their movements are picked up by the phone's camera. In another game, the phone can be tilted in different directions to guide an on-screen ball through a maze.
My theory is that this is a ploy to boost sales of cells phones—because all that punching, weaving, and swinging is going to get a lot of phones broken (including by irate recipients of accidental punches on crowded subway trains).
Oh, and my apologies if upon clicking the above link you were subjected to one of those dancing-silhouette ads. Let's think of it as an opportunity to practice not letting things annoy us.