Nice thread RR.
The two most influential mentors for me were my Grandfather and a maternal Uncle. Both woodsmen, canoeists, hunters, and anglers.
My Grandfather was one of those guys you could leave at the side of a lake with an axe and a pocket full of seeds and come back in a year to find a cabin, smokehouse, and little garden. He had all kinds of knives but I remember him carrying a Case "Jack knife" as an EDC and Marbles (?) Woodcraft (?) fixed blade as a "deer knife". The two blade "jackknife" was his primary blade.
My Grandfather gave me my first knife, a SAK. Don't have that one anymore.
My uncle carried a Buck 110 and, later, a Schrade or Buck fixed blade. He probably carried a pocket knife as well, but I associate him with that 110. He's the reason I still have and favor the venerable 110.
My Uncle gave me my first fixie, a Schrade Old Timer Woodsman. Stout as hell, but a nice knife.
I don't think the multiple blades were all that important to these guys. I suspect the idea of having different blades for different purposes was more theory than practice. Maybe stockmen really did like having a sheeps foot blade in addition to a long clip and a spey. Maybe not. I suspect that marketing has been an influence ever since the first flint knapper started trading for meat: "yeah, but this chert knife has two edges..."
I like my Case Trapper, but the elongated spey has never really seemed that useful, probably a single bladed Jack would be just as handy and weigh a little less. Certainly the popularity of the single blade SAKs suggests that the contemporary user doesn't need 3 different blade shapes as much as the old guys seemed to think they needed 'em.