Killzone 2 kill count and KDR?

Normally I dont pay too much attention to my KDR (kill death ratio), I care more about total points, but when I was checking my rankings for the week I noticed that my kill and deaths were about even, and at one point more deaths than kills. Now, I am far from a beast when it comes to FPS's, but I'm definetly not a slouch. Now a normal match (and I only do full warzone, no 200k30m bodycount here) I will average 35 kills and 20 deaths, sometimes even better, a few times maybe worse. Add in the mission points because i actually try to complete objectives (i know right!) and heal people/shot down bots, etc. and never am I below 125 points a match win or lose. There is no possible way, if the stats are correct at the end of the match, that I should be even overall for the week. Not if I am CONSISTANTLY getting 10-15 more kills than deaths every game. I've been keep count myself and I should be +75 kills this week, and not +5 or 6.

Anyway, the question, are solo kills the only kills counted and assisted kills aren't? Because this is the only explaination I could think of, and even then that barely makes sense, cause if it counts as a kill during and at the end of the match, it should count overall for the week. Has anyone else noticed this, or am I trippin over nothing?