I tend to think a lot of it is because Spyderco knives are kind of quirky and while they do have a lot of models most of them are comparable (obviously not the Kiwi and Delica, but Military, Manix, Delica, Endura, Police etc. have a lot in common). Benchmade, on the other hand, has the Snody Resistor and AFCK. If someone says Spyderco, I think triangular blade with opening hole (which, if I may so so, is probably the most practical and best looking blade for every day use that I've ever seen

) with handles and a lockback. If someone says "My Benchmade...." I don't know what they're talking about, because that could mean anything from a Griptilian to a McHenry Williams design, if that makes sense.
It's a lot like saying "My SAAB" versus saying "My Ford". SAAB's have a connotation (or used to) of odd-looking hatchbacks, and whether you had a 9000, old 900, new 900, or old 9-3 people tended to associate them with the same basic shape. Ford, however, has had a lot of different styles over the years, and people don't know if you're talking about an F150, Tempo, or Focus wagon/hatchback.