if its realistic it possibley points to the construction of the panels. possibly the panels are layered to reduce weight and just use minimum amount of rivetts ?

Great question though !

edit, found this image which supports the single lines of rivetts. the rear sections covering could be thicker, maybe have tongue & groove system etc. i say its realistic given same is seen on this image.

http://i72.photobucket.com/albums/i1...AS-detail2.jpg