I think Sammy has explained this before... the problem is that the aim and distance have to be correct at the point of contact, rather than at the point of hitting the button. So you can be lined up perfect for a knife and hit v, the person moves before you are at the peak of your lunge, so you miss. I have the same issue with shooting people sometimes.... they can be sat in a corner and I empty a clip into them, they then turn into a car and blow me up. It's why I get so frustrated with this game that I don't play that much now.
Insurgency seems to have almost no latency issues. If you have someone in your sights and you shoot, you tend to hit them 99% of the time, regardless of ping difference and if they are running, you only have to account for bullet travel, COD4 you have to account for bullet travel and ping difference. I have to aim 10 yards in front of some people, but only 1 yard for others in COD4.