[DennisP]

What I mostly see from EVs is varying the number of motors. You get the manufacturing cost reduction on your motors without having to actually over-spec your base model.

Even this isn't the whole story though, at least at the high end. The Model S Plaid has an extra motor but also uses different rear motors, designed to be more efficient at high RPM. And Tesla puts a lot of emphasis on parts commonality in general.