Being able to have both styles was one of the reasons the second "Clone" head was created, as the old Noboto head design also had a point where it was bumpier and a bit more skull like.
Noboto, meet Noboto.
EDIT: I forgot to mention that Reverse Noboto (Otobon?) up there is sporting a few tweaks to his core build, with a flipped chest (macho style), reversed thighs (to stand up straight), flipped biceps (bent for battle) and a swapped belt and scarf (for sleeker lines and, uh, pockets on the back of his head).
I imagine this form being favored by the more aggressive Noboto Clones out there causing trouble.