If that's the case then it's really your insides shattering from the impact that kills them and not gravity.
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If someone suicides off a cliff it should still award the 5 points to the team that had gotten the last hit on that person, like in league of legends with executes, if they haven't been hit in 10 seconds then no credit is given.
You jumping off and getting pushed off are two different circumstances. If I'm clever/lucky enough to shove you off a cliff to kill you, that still speaks of my skill/fortune. Furthermore, if you see no way of escaping with your life intact (making you choose between the cliff or the sword), your attackers have won by forcing your hand (checkmate!). Being able to jump off and kill yourself doesn't mean that Titan didn't beat you.
In League of Legends at least, if you're killed by a minion, turret or monster, the last enemy player to damage you gets kill credit. Only by completely escaping combat for several seconds (a long time!) can you reset this. I'm not sure how many other PvP games do this, but it seems accurate to me.
In the end, it's up to SE to decide if they want to allow Kill-Denies or change the system to be more intelligent about gravity-murder. It doesn't really matter as far as winning and losing goes, but it strikes me as weird.