I think it hits pretty close to home though.
I think it's not that bugs flip over to die, I think it's that, when you find a dead bug, it is more likely to be on its back for several independent reasons, some of which are mentioned in the link.
- They fall off the wall, or off whatever.
- They are top-heavy - especially since their legs curl up under them when they die.
- It is possible for them to start on their feet and get flipped onto their backs after death, but impossible for them to start on their backs and get flipped over onto their feet.
- Many may die BECAUSE they fell on their backs and can't right themselves.
Ultimately I think, as a rigid object, they are much miore stable on their backs. The above are all randomizing factors that favour this position.