Well, they're paying 21 million dollars to: 1) Continue using the clock. If they lost the lawsuit, they would have to stop. 2) Not admit they are wrong. 3)

Well, they're paying 21 million dollars to: 1) Continue using the clock. If they lost the lawsuit, they would have to stop. 2) Not admit they are wrong. 3) Avoid a very public trial that competitors could point to and say "Apple copies too!" All of those are probably worth more to Apple than the actual lawsuit damages.