I thought that would be part of the reason. The ends of the rails could be straight up and down though so it would line up with the rest of the grid.
I don't know if you do any work with wood but it would be like a board with miter cuts on both ends. If you lay the board flat, both ends would be angled ( \===\ ). If you put the board at the proper angle, the ends would be vertical ( |\\\| ) and the center would be angled.
Just something to keep on my wishlist for 4.0! I shall stop pestering now until I have another legitimate question