COD4 Observation

I noticed an interesting phenomenon playing Call of Duty 4: Modern Warfare over the last year or so. It seems that when people in a hardcore deathmatch (hardcore because you are susceptible to being killed by friendly fire), they seem inclined to message you in the event of a mistake.

Let's say you accidentally kill a team member - something entirely possible in the midst of a heated firefight. You can be assured a quick message will soon hit your inbox with "WTF?" Let's say someone kills you. This situation rewards your inbox with, "sorry 'bout that" or something similar.

Can't we as gamers just assume that people make mistakes and not get so hostile or apologetic in the event of either taking place?