4-doors are lighter than 2-doors?

So I found something out interesting... my 2006 G35 sedan is lighter than the coupe version. I want to say the trend is the same with the BMW 3-series where the sedan is lighter than the coupe. My guess is the door of the coupe, which is much longer, also has to be made much stronger to absorb a side impact. A sedan has a b-pillar more in the middle to take the hit, so I'm guessing the doors of the sedan are much lighter. Also, coupes tend to have a much bigger rear windshield and glass is heavy!