RE4 doesn't reward for headshots
"It turns out that those folk who'd played Resident Evil 4, which rewards points for headshots, continued to aim for the head, with an average of seven cranial hits each."
Like Koyaanisq said, RE4 doesn't reward head shots. It's the most inefficient way of killing enemies in the game, as it takes a lot of head shots to kill an enemy and therefore a lot of bullets (of which there are a very limited supply in-game). As it's such an inefficient way of killing enemies in-game, it is not rewarding players. Players need to sparingly use ammo, which means disabling enemies with shots to limbs and moving in for melee moves.
Also, the more enemies you kill, the harder the game gets and so it doesn't reward killing. In many instances you're better off outrunning enemies.
The number of places I've seen report on this report and state that Resident Evil 4 rewards headshots... I wish people would actually research the game a little first. You don't have to play it, but most footage of the game doesn't show players concentrating on head shots.