I think you are also missing some data. Sentras only came in a manual tranny up until about 8 years ago, the base model had no AC, power windows power locks, power trunk release and so on, things that are all standard even in the base model now. You can't compare the weight of a base model from 19 years ago to now and say its only because of safety stuff. With today's modern materials, there is no reason we can't get it down to that weight if you strip all the amenities out of it actually compare model to model.
Strange, I looked at the traffic fatalities numbers, from 94 (thats as far back as it went) to 2006, traffic deaths went up almost 10%!!! Went from 36,200 to 39,200! I wonder if that is due to speed limits going to 70mph?
Just wondering, since our vehicles got safer, yet fatalities went up.