I think you mean that they defend the hole because it has become "synonymous" with the Spyderco brand is all and that communicates innovation and quality to buyers (characteristics that are valuable), correct?
No, not really. I originally typed that sentence to say: " Probably
part of why Spyderco defends the thumbhole trademark so aggressively." but amended it because I was getting too many "part of" comments in that paragraph. In retrospect, it was more accurate with "part of" in place.
I'm sure that if you asked Spyderco they would have a response very similar to what you said and I wouldn't argue with them or you about the accuracy of the statement. But what I was getting at was that I think another part of it is that the size/shape of the Spyderco thumbhole creates distinctive and generally similar blade shapes which are easily recognizable--unlike other smaller/different shaped thumbholes which generally have no effect on the overall blade shape.
So not only is the hole strongly associated with Spyderco and not only is it an easily and widely recognized feature, by necessity, it also creates a general similarity in the profile of Spyderco knife blades which creates a brand "look".
The three knives in question are perfect examples of the size/shape of the thumbhole affecting the blade profile. All have thumbholes, but only the Spyderco thumbhole's shape/size necessitated a humpback blade. The other two knives have blade spines that align with the handles and have no humps.
If you were to overlay the Iconic and the GM1 I think the profiles are nearly identical, but the Spyderco edge profile and choil and flipper and the lock choil are going to give a different outline.
Right. So if the profile/outline of the open knife is the defining characteristic then that would be a definitive statement of similarity.
If one were to factor in the profile of the knife when closed, and also claim that handle appearance is a very important aspect of similarity then the Spyderco and Iconic would probably be the closest matchup of three since all three knives have pretty similar profiles when closed (if one can overlook the humped blade of the Spyderco) but only the Spyderco and Iconic both have one synthetic side and one metal side to their handles in the original picture set.