Don't know about this car in particular, but there's also the issue of safety. It would be possible to build cars that get better MPG if you made them lighter, but that'd mean you'd have a much higher chance of dying in any form of accident. Also, there are other ways to get great MPG but you may end up sacrificing other aspects of driving (I remember in my business class, we watched a video about changing your paradigms. In it, there was a car built by fluid engineers that got something like 1000MPG, but there were things like it had very little acceleration, could get to a max of 30MPH, etc).