The Decepticons Pretender shells were not meant for camouflage (is my spelling correct?) but rather they used it for added firepower, and armor and shock value ( a psych warfare kinda thing) thus they used the theme of monsters, spikes and all. Such was not the intention for that particular technology when on the autobots end of the spectrum, its for disguise as these shells allow them to "shrink" ( read:mass shift) into humanoid sized, well ....humans as seen in the japanese TF series Pretenders. This is so they can operate easily on earth without drawing much attention. Decepticons couldn't care less hence monsters - good for causing mayhem and wanton destruction.
As always the varied way of thinking is very much evidently displayed by both factions with regards to the technologies they use, pretender shells included. Take for example in the G2 Marvel comics. This was thought of by Prime himself with regards to "warworld" - A mobile moonsized battle fortress of mish mashed stolen technology from dozens of conquered planets by the decepts. Prime states in his thoughts - were the Warworld is concerned, He ( in extension autobots) are thinking communication, while Megatron ( in extension decepticons) is thinking weapon.. which pretty much exemplifies it up with regards to views of the gimmicks/ technology for each side. Hope this helps.
Wanted AM partner Vanguard, Myclones Dirge, G1 Victory Leo, e-hobby Dark scream ( the black version), e-hobby Magnificus
Parts- AM partner Basher-side guns, G1 Actionmaster Elite Windmill's blades[I][B]