I don't fully buy this - if you optimized for aerodynamics and safety you'd get cars so far outside the aesthetic it would be ridiculed. No-one is making fun of the new USPS trucks for lack of fuel efficiency, they're saying it looks like a platypus. I can see a weaker version of what you're saying, that the intersection between the aesthetics a mass car market would accept and an acceptable fuel efficiency/safety yields a very narrow design space.
Maybe I wasn't clear because I wasn't talking about doing anything, or suggesting that car manufacturers do anything, just I don't think this comment is the full story:
> Modern cars are all built to be as aerodynamic and fuel efficient as possible, and the constraints are virtually the same, so the designs are very similar as well.
