Many, many people. But I didn't think anyone played Killzone 2 anymore, or could be bothered to complain about it. It's nearly a year old now.
As for not knowing it had splitscreen, that is entirely your fault for not doing research. Though to be honest, if it ran like it did with ONE player playing at once, with TWO it would probably be unbearable.
I liked the game, very much. Better than *ech* R2, anyway.