Anthony,
Of course, preserving flatness is one of the reasons to have solid casebacks, but Piaget is not always blindly pursuing flatness. They decided to increase by 0.15mm from the 9P to the 9P2 movement to increase stability.
What is surprising is that even watches with something special to look at, did not have display backs e.g. the following movement was found in the 120th Anniversary watch with a solid caseback. Go figure!
Must be Calvinist thing....so modest!
Regards,
MTF
