I think, if you are only selling physical stats and skills, you are giving a big, big advantage to players who are just good roleplayers. (And I say this as one of those good roleplayers, imho.) They already have that advantage. They make friends faster, better. They get into more plots and involved in more things. If they now don't have to buy their social skills and just play how good they are, then now you give them the opportunity of being powerful combat beasts and social masters at the same time, because where else would you put your XP?
I think you'd lose a lot of the archetypal characters you are wanting because yeah, you could still /play/ Littlefinger if you are good enough. But now you can play Littlefinger without having to back it up with stats, and also make Littlefinger a master magician or knight or etc.