Well, blueprints are great and all, but things often change when it comes time to actually build things (if that was what the blueprint really intended).Ah - so I was wrong, then. The bars looked to me like they were supposed to be folded on the blueprints.
I imagine the builders found it was a heck of a lot easier to do the edge folds on the back plate and then lay in the solid bars, rather than do a crazy number of back and forth bends to make all the "bars" as ridges on a single piece of sheet metal.
That'd be, like 20 bends on a little 4.5" piece of metal!
And there are 4 vents per robot!
And they made 6 robots for the first film!
That's almost 500 bends! Just for the vents! Oi!