RG Live WotLK 3.3.5a

sollte nicht durch offhandattacken proccen

http://wowwiki.wikia.com/wiki/Killing_Machine

KM procs on mainhand only, otherwise you would absolutely have a point.

Also, a reason you forgot to use 2h is Rune Strike. It does much higher damage with a 2her and cant be dodged/parried.

Not to stomp on your test, but Blizzard has said and extensive testing on EJ has confirmed, that the offhand can't proc KM. I find it highly unlikely that your test is real and that you controlled for all factors.

http://www.arenajunkies.com/topic/59127-dw-or-2h/