I never had a problem with this in NV.
With NPCs killing other NPCs
or me killing an NPC because I accept the consequence that they might be a quest giver.
FO:NV isn't exactly the same - it had such a complex web of quests, that conflicts were inevitable (since you could work for different factions). Like, you're doing Quest X ("go kill Bob"), and when you kill Bob... it says "you failed Quest Y". Because, if you were working for Bob's faction, you would have gotten a quest from him.
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Personally, I never had a problem with the essentials in Oblivion. Not having major quests fail out of nowhere, because some NPC ran afoul of stupid AI.... seems like a good thing. (Of course, I also never randomly killed people in towns, so "OMG, I'm so annoyed that I can't slaughter all the important NPCs!" never became an issue. :shrug:)