Maybe when sentient robots are added to GH2, they should be given a point-based system, similar to normal character creation? Auto-distribute some, and let the player decide on the rest, with robotics skill determining what percentage you get to distribute yourself, and skill and material determining how many points are given.
On machine charisma...
If you could read the thoughts of everyone around you, not through telepathy, but through recognition of every subtle sign and inkling of body-language telling you what they feel, do you think you could play to their emotions? Assume you could keep a straight face and use any tone or level of voice you want, and that you can perfectly mimic whatever body posture you need. A sentient humanoid machine would have access to all of this. The conversation skill in game mimics 'technique', but charm is their raw ability to be liked, to use empathy to get where they need to be.
True, a human politician could talk the pants off a machine with no experience interacting with humans beyond base programming and very limited interaction(with it's creator, for instance). However, come back in 10 years after the AI has spent significant time learning about humanity, and it'll out-talk and out-impress any given politician without trying. A machine could read and react to a person far better than another person, giving the ability to compile a sort of psychological profile on-the-fly, which would be a huge edge in a conversation.
It isn't charm, or charisma in the standard sense of being someone people naturally like, but it leads to the same thing and works in much the same way. A person probably couldn't pull it off because we can't mask our emotions very well, usually, and we can't take in every twitch or shift in the other person to determine what they could be thinking.