I noticed all my Insane Sims are paying the bills with their left hands lately. I noticed it when I played with Charlie Sheen as a Sim (and this is just my beta testing game before I create a story about him) he wrote with his left hand. Dorie and her husband Gus also used the fork and paid the bills left-handed. Sim-me has star quality and is eccentric and she paid the bills left handed (real me is a lefty anyways). So my guess is that the traits that enhance oddness creativity and recondition are the ones that promote Sim left-handedness. (Virtuoso, Artistic, Insane, Star Quality and Eccentric). As far as Leto's theory, I will play the Hart family, Lola Belle's household (Lola is an artistic virtuoso), Meadow Carpenter-Rhodes (insane Riverview townie who's also a virtuoso). EA i think figures real life left-handed people are typically more odd and creative so they played it into their Sims.