You are right especially in terms of the pricing. I also have them both and I enjoy to extract ideas and elements for inspiration out of them but to me as industrial designer I personaly prefer simons sketches because in my eyes the choice of line spacing, the shape proportions and the design decisions overall are technically mature as they are in robertsons books. Simons book also shows thumbnail drawings before he gets to the polished sketches where you can see different stages on the way to the final designs.
Yes, Scott shows nearly every approach compared to Simon because he wants to show all the possibilities. But I think the design style matters a lot and not soley different techniques. I also have the book “drive” which is very much oriented by cosmic motors and there you can see the difference in the design even more. But as mentioned, that´s my personal view.

Berkey even better, though the prices of his books online are astronomical (much like the out of print Mead books).