I meant how you approach to complete the quest. Not how you approach the guy to get quests.
I really don't understand what you mean by that. First you said: "And you can only approach those quests in one way", when clearly a lot of quests can have different outcomes based on what you do and what dialogue options you choose. Some quests aren't linear as you can begin some of them very differently such as just stumbling upon a story quest in the wild when you go about exploring rather than picking up the quest in a more traditional way.
Now you're saying it's the approach you take when completing quests? well isn't just personal play-styles and personal choices in the dialogue? Someone might be more focused on melee skills but someone else might be more focused on alchemy and bombs. Some players may try to exploit some npcs via dialogue options for money, others may not.