It is my view that no mechanics can simulate human interaction. Even today with thousands of hours and millions of dollars the best that science been able to produce are a few clever simulations of human interaction that work very well for specific circumstances. For example Siri on Apple iOS devices.
One of the strengths of tabletop RPGs is having the human referee to adjudicate the actions of the characters as they interact with the setting.
You do have to have some type of mechanics because we have players with characters that have skills and attributes better than their own personal skills. In my experience, it is easier to come up with mechanics to deal with attribute that deal with physical interactions like strength, dexterity, and constitution. And it is harder to deal with the mental/social ones like intelligence, wisdom, and charisma.
My technique is based around this concept; while the player may not be as mentally/social adept as his character, as the human referee, I have complete control over how the setting/NPCs respond to him. So in the absence of a compelling reason, I will act as if he was the smartest or most socially adept person in the room if his attribute/skill warrants it.
A compelling reason for me means that the player has totally misread the situation to the point that he is not just way out in left field but not even in the ballpark.
What I use to decide how my roleplaying plays out are the circumstances of the encounter, the result of a skill/attribute check, and my notes on the NPCs involved. For example if a 1 or critical failure is rolled on a check, I will roleplay it as if it is a disastrous social encounter. If a natural 20 or critical success is rolled, I will make it work out even if the player is out of the ballpark in how he handling the situation.
The downside of course these are all highly subjective criteria that benefit enormously from personal experience. Both from life and time spent refereeing campaigns. This can make it daunting for a young referee just starting out in tabletop. Hence the appeal of social mechanics as an aide.
I would tell the young or new referees is to rely heavily on the stereotypes that they know already. To sit down prior to the campaign and make a one or two page list of notes on the different types of NPCs and how they would act when roleplaying them. Use that as your starting point. Eventually as you grow older and gain more experience, you will develop a greater range in how your NPCs act.
I think most RPGs, even detailed ones like GURPS, would benefit from more advice and less rules when it comes to social interactions. I will say for GURPS, I do like their reaction tables. While I think as a rule mechanic they are so-so, I do think they are good lists of possible outcomes for specific social situations ordered from worst to best.
When I hear that a RPG, say DnD, is lacking in social mechanics I view it as being short sighted. The one of the rules that ALL RPGs share is the fact that the game has human referees adjudicating the actions of the characters as they interact with the setting. As all social mechanics are inadequate to simulating human behavior, the need for a human referee handle social interactions for D&D is no different than any other RPG.