The designer's *Intent* is a key element here.
GTA does *let* you do some pretty nasty things, but that isn't the *point* of the game. Killing a police officer to watch him die isn't something you'll be rewarded for: in fact, it just makes the police try harder to catch your avatar.
iSealClub is clearly making the clubbing of seals the *point* of the game. This changes matters: in GTA, the player is actively *penalised* for behaving badly.
The developer's game is both derivative and tasteless—he would have had the same result from Apple if he'd made a game about raping children. Sure, no *real* children would have been harmed, but it's hardly a game Apple could put on their iTunes Store until they have airtight age ratings and parental control systems in place.
Contrary to popular belief, games, movies, TV and stories *do* affect the consumer. That's the whole damned point of making them in the first place. Spielberg didn't make "Schindler's List" for shits and giggles.