The copyright pertains to Graphic works - from the Act:- "'Graphic Work' ("any painting, drawing, diagram, map, chart or plan")
Reproduction is the exact issue - That is why it is called copyright. Should one print those plans in a book, they will have arrived there via a computer. And copyright law would very much still pertain.
Patent applies to the designs described by the drawings, Copyright applies to the drawings themselves.
You have quoted the US Copyright Act - I am more familiar with the UK equivalent.
There is clause in the UK Act that seems equivalent to the doctrine in the US one, so that reproduction for academic or research use is indeed allowed. However, it does clearly prescribe the use of appropriate acknowledgement in this circumstance.
There's no hidden agenda - just a gentleman's agreement to honour their request. They are not aware of any more material, but it doesn't mean that more rummaging won't unearth it. To allow us to rummage in their archive - which is on their HQ and factory site - we need their goodwill.
AAaaanyway - I know it's all very arguable - and I am not a lawyer. Having said all of this, I would always be minded to acknowledge my sources even if there wasn't anything to gain nor legal imperative.