In one of the links you posted, they were talking about the algorithms used to make that happen. Each sim is "consistently random". They randomly get a "style" of many possible, and continue with that same randomly generated style throughout their lives. I thought this was brilliant, but I'm unsure if it has anything to do with traits at all.

Possibly because each set of traits is what makes a Sim unique. However, I still wonder how Sims with the same exact set of traits will still be the same as each other or still uniquely differently. I hope they still get to be different to make it less predictable.