I don't know if they could restrict the actual number of lots per performance settings (I have never really heard of anything comparable in other games either), but they could probably do more loading screens at lower levels. For example, at lower settings you would then need a loading screen to access the "open" part of the neighborhood where the townies jaunt around. Basically, straight Sims 2 stuck to home lot on the most basic settings.
This being said, I do feel the video beat around the "constraints" bush. Too hard on performance, too much space, etc.
