But in a game this makes no sense because you aim with the hud crosshair, you should always have a perfect shot if your crosshair is lined up with the enemy.
Shots becoming more accurate when you look down the sight in games is just weird and wrong.
Well you wouldn't have a perfect shot with the crosshair lined up because the crosshairs are usually there to indicate bullet spread. However, your bullet spread should be the same with ironsights up - but what a game is simulating with ironsights being more accurate is your ability to control the recoil with the gun nuzzled in your shoulder.
Having guns fire the same whether you had ironsights up or not wouldn't work in games imo.