It's not a gimmick if the person who wants it ends up loving it. To the batman enthusiast that batman lolipop was a nice lovely little treat they happened to find in the store they strolled into. Nothing less, nothing more.
As long as it's not a flash in the pan then I don't think it's a gimmick. The wii was not something built for just one game, it was developed intentionally to alter the function of a multitude of games. It's not a gimmick because it wasn't ever intended as a gimmicky one-off pony trick.