Billy,
I think it's foolish to say that Canon and Nikon (and maybe Olympus) are the only products worth considering. The paragraph you quote doesn't quite say that, but that seems to be where it's going. The truth is, there are lots of reasons to pick a camera brand. For example, if you've been using Pentax all your life and have a ton of great Pentax lenses, then of course, buying Pentax would probably make sense, at least economically.
But the rest of the statement is basically correct. Canon
is the market leader, and not just (as your source says) in "advanced amateur and professional" photography, it's the leader in every area, as far as I can tell. And there definitely are some major advantages to buying Canon or Nikon. It's not just that it's possible to rent Canon and Nikon lenses. There are also more Canon and Nikon lenses available for purchase, both new and used. Take a look at Sigma and Tamron's sites on the Web: just about every lens they sell has a Canon and Nikon version, but only some are available with Pentax mounts. Buying Canon or Nikon, you also have more bodies to choose from, including full-frame digital bodies. Among other things, that means that there's room to grow (as in, you could keep buying more and more expensive cameras); with Pentax, on the other hand, you move up from the K100D Super to the K10D and you've hit the product line's ceiling. This would be fine if the K10D were clearly the greatest camera available for any use, at any cost -- but it's not. There are more accessories like detachable flash units available for Canon and Nikon cameras. Almost every book on the market about digital photography seems to assume that you have a Canon or a Nikon camera. Join a camera club, most of the experts there will be using Canon or Nikon equipment. And the Canon and Nikon cameras are not bad, not bad at all. A the low-end and even perhaps in the middle "end" of the respective product lines, Pentax competes very favorably. The K100D is a better camera in itself than the Rebel XTi. The K10D competes very favorably with the Nikon D80 or even more expensive models, simply in terms of the body and its features. Pentax lenses are excellent, if you can find 'em.
So if you compare this camera to that, Pentax is a very strong option for consumers. This is especially true if the Pentax camera being compared is a K10D. If you compare systems to systems, on the other hand, Pentax looks a lot weaker. This is never going to change.
But does that mean that Pentax is a bad choice? Not at all. There are excellent reasons to buy Pentax -- but most of them have to do with money. In the conventional DSLR market, the Pentax K10D is far and away the best value for the money, not because the camera itself takes better pictures than, say, a Nikon D200, but because the camera is very well designed, because it takes photos that are as good as cameras that cost a lot more, and because the selection of lenses is good enough to make it a viable choice for many photographers. The K10D's ergonomics really are great -- but if somebody gives me a Canon 5D, I'm going to use it. Would I care about shake reduction in the body if I could afford to buy shake reduction in my lenses?
The fact that the reasons to buy Pentax have more to do with money than anything else is slightly embarrassing, I think, but it should not be. The truth is, all of the major manufacturers now make terrific cameras. Different models have different limitations, but if, in the end, it's about the photos rather than the hardware used to take them, then almost any brand will do. If I were a zillionaire, I'd own twenty different cameras, made by half a different manufacturers. Which one would I carry around most? I don't know. I think it's interesting that Ken Rockwell, who apparently
does own dozens of cameras, is so fond of the
Nikon D40.
I don't know what to think about Olympus and the four-thirds system. Yes, it's innovative. It's been designed from the ground up with digital photography in mind. But it looks to me as if the engineers at Olympus were thinking mainly about lenses, rather than sensors -- and it turns out that sensors are where the real action is, at the high end of the market. I would not be surprised if the four-thirds system succeeds and establishes itself as a great choice for amateurs and hobbyists. I don't see it making any inroads among pros. That's not a knock.
Will