Personally, I think this is a great exploit that should be kept in. IF you don't care about lore and suc hb and just want to win all fights, then by all means turn the battlefield into a giant trap before killing everyone without talking to them.
The game IS meant to be like a tabletop in ways like this, where while the NPC is distracted you can sabotage his plans for battling you or w/e.
I agree that chatting to distract NPC's should be kept in for thieving and pickpocketing. But it does not make any sense for NPC's to not react and engage in combat when they are attacked just because someone is talking, and that goes for the NPC you are talking to as well. If you're attacking his allies, he should break off and start combat immediately.
