Anything branded Minolta, Pentax, Fuji or Olympus does not get the credit it deserves. For most people, there are only two names: Canon and Nikon. Those two brands have historically been the only ones which made a consistent investment in professional support in photographic venues. A professional photographer I know uses Canon only because he can find assistance near the foot-ball pitch. You have a problem with a lens or a body: Canon representatives are there, they can repair it on the spot or hire a substitute.
I do believe is this kind of massive investment which made Canon and Nikon the choice of those kind of professional photographers. And once this choice is wide-spread, you will find that lens renters have a large assortment of Nikon and Canon lenses and a small choice of other mounts. Another reason, for the professional, to spouse Canon or Nikon. Minolta and Pentax tried to invade the professional market (XM and LX) but, as far as I know, were not prepared to follow the professionals on the pitch, to be there when they were needed.
The layman sitting in front of the TV sees professional photographers at work only in the old same occasions: sport, star-system events, fashion. They see Canons and Nikons and they think it must be better quality.
In the Eighties I was an affectionate reader of a magazine which published 2-4 MTF tests every month, typically direct comparisons. Nikon and Canon lenses were typically lower in MTF results than Minolta and Pentax. The plain and cheap Nikon ES 50mm given with cheaper Nikons was much better, optically, than the 50mm Nikkor of the time. The only lenses which were constantly a notch above any other optically were the German ones.
The magazine explained the different performance between Nikon ES and Nikkor is a result to be expected. The SE series was a newer design. The Nikkor was basically the same design of the Sixties. The Nikkor was superior in ruggedness and serviceability, each lens (lens group) having its own bronze collar to make a realignment easy and fast. If you drop the 50mm Nikkor, a technician can open it and realign it without problems. Cheaper lenses do not allow that. Minolta and Pentax typically had better design and optical performance (until you dropped them on a hard floor, that is). Nikkors and lenses for Contax and Leica (not so much Canon) were much better built mechanically (Zeiss and Leica also optically).
What the professionals look for and find in Canons and Nikons is not strict optical quality, but other advantages, such as service and serviceability, which is typically not so interesting for the normal user.
Fabrizio
PS Also, professional cameras such as the top of the line (F3, F1, XM, LX, etc.) typically are sold by the factory under cost, i.e. at a loss. Factories do that because in the long run they will recover the money by lenses profits. It's a long term strategy. A firm must be prepared to make a courageous long-term investment to enter the professional market. Minolta and Pentax, and especially Olympus, were not persevering in that effort.
