http://wow-europe.com/en/pvp/pvp-article-part2.html
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In fact, if you kill an NPC who is not PvP-enabled or who is PvP-enabled and trivial, you will gain a Dishonorable Kill.
That sounds kinda fishy... There are lots of NPC's in the world who are not PvP-enabled, actually that's what PvE is all about..... :P
They also stated that they weren't initially planning on doing anything with dishonourable kill points, primarily because that's the main way to start a PvP battle on non-PvP servers.
That's not really true though? You typically start a PvP battle by killing PvP-enabled enemy NPCs, which are honorable kills. Their definition of dishonorable kill includes all NPCs that you are supposed to kill as part of quests, without going PvP.