depends on the type of game.. if it's a game that can easily be cloned, then it probably will be if it shows any signs of success. If it's a game that takes months and months to recreate, then you're already ahead of other people, and if your game is successful, then who cares about the imitations- people will want the original.
Making easy quick simple games just makes it easy quick for others to copy..
So in other words.. the simpler it is, the less can get in the way of others cloning it..
the more complicated it is or time consuming to make, the more gets in the way, and people that spend considerable amount of time on it would probably want to personalize it a bit and not copy everything.