Like much of the history of technology, the rise and fall of various photographic giants is an interesting thing. In the mid-1960s, the market for SLR cameras was utterly dominated by Pentax. Pentax owned more than 50% of the SLR market and were driving innovation and change, such as TTL metering. Then they blew it... Well, not entirely, they still produce really good equipment, but they lost market dominance. I think some factors played a role:
Pentax was slow to abandon the M42 screw mount (also know as the "Pentax Mount") in favor of the bayonet style. They've been historically reluctant to drop legacy support which, in some senses, has now probably kept them alive since their modern lens lineup is lacking. Anyways, Nikon beat them to the punch on the bayonet mount and introduced the first real camera system, much more interchangeable in areas like focusing screen, etc. Big innovation, drew in the pros in a large way for the first time in the 35mm segment.
Canon beat them all to the punch with the A-1 in the late 70s, the first with, what amounts to, an amateur mode and that baby sold like hot cakes. It basically brought SLRs to the masses and the masses bought it. Pros didn't so much, but cash helps fund innovation and the A-1 would give them cash.
Pentax couldn't get their head around the idea that 35mm was now a professional format. They really clung to the idea that medium format was professional, 35mm was, at best, advanced amateur. Whoops. Not surprisingly, professionals aren't always shooting on a tripod in the studio or on a tripod shooting that mountain scene, they do other stuff, and lugging around a medium monster with lenses isn't a lot of fun. You could just see the newspaper photographer popping up the Pentax 6x7... Nope. Net effect, Canon and Nikon started building systems to attract professionals, Pentax did not, not in the 35mm space in any event. So, when these pros give camera advice, the advice is going to be on what they know, kind of like it is today. You tell two friends, they tell two friends...
I didn't mention Minolta, Yashica, and others in all of that. They certainly played a major role in the development of the SLR, but in a lot of ways you can trace the rise of Canon/Nikon with the fall of Pentax, the others were just kind of there, taking their slice in a kind of constant way. Much, in some ways, as it is for Pentax and some others now.
So, I think the end effect on this one is a combination of a whole lot of factors, which isn't surprising. In some sense, the answer to most of your questions in your last paragraph are: yes. I don't think they necessarily have the best technology though, but they certainly don't take a back seat there either.
That's my take, in very much synopsis form, of what I see as a big piece of the history behind the resulting dominance of the big two.