I'm not saying it isn't well built, but with small cars, the profit margin is pared to a minimum, and the bean counters will always try and cut the quality of things to save a few quid.
IMO the real problem with the 500 is not so much build quality as component quality. Most of the problems on this forum aren't the result of the car being incorrectly assembled, they're down to components which have failed prematurely, fallen apart, fallen off or been recalled.
Again, just my opinion, but it seems the bean counters at FIAT have chosen to build the cars out of what may well be the cheapest and shoddiest parts on the planet. Even with the best manufacturing facilities in the world, you can't make a silk purse out of a sow's ear.