They're obviously going for cartoon-likeness, and as griffin pointed out, that's how the missile launchers on Bluestreak looked like in the cartoon (and comics) -- they were pipes! Prowl was drawn without shoulder mounted launchers in the cartoon and comics anyway, so if you want show-likeness with him, you'd just retract them. That's how I display my Henkei Prowl and Streak. It's not TakaraTOMY's fault that they look like that... that's how Floro Dery designed them!