It's got to do with the particular brand of hit detection: client side. Basically what happens is that what you see on screen and shoot at will be translated to the server, and basically that means that due to latency, the guy you're shooting at is actually ahead of where you see him. However, because there's CLIENT side hit detection, the server takes your data largely to heart and even though that guy you just downed thought he was behind the crate, you saw that he died a good meter from cover. As you can imagine, increased latency compounds on this. It also works both ways, as shooting at someone with high latency will have the same effect as someone with high latency shooting at you. The only actual advantage you would have with a low ping relative to your target would be in a one-on-one firefight. Because your kill data gets to the server before theirs, their death is registered first.
This has a number of advantages and disadvantages, from allowing a smooth game experience even when you're playing oversees servers (like I recently have been with some people who actually try and get mumble chat going) to removing most of the major advantages to playing a local server. I won't really go into the nitty-gritty, but be wary: the only way to guarantee you won't die after making it behind cover is for everyone in the server (and I mean everyone) to have a low ping.
But, so you know, it's not the hit detection. That's actually much, much improved over BC2.
