I Agree with this it's pretty fun to be able to see who made the killing blow on that difficult boss, not to mention it helps you see who are actually your more effective characters, sometimes you're surprised by the results. The way it worked on the IE game would be perfect IMHO, but they could also go for more detail such as in RDR, where they show how many of each enemy you've killed, accuracy, etc.
I don't usually take notes while i'm playing but I've seen some people do it so a tool that would allow you to do something like that would probably be welcome too, though probably not indispensable.