Hi, John!
I am not certain I can answer your question completely quantitatively, but there is a qualitative response.
From your question, it would seem that you are interested in cameras that must be housed. I.e., Sea & Sea, Ikelite and others in the u/w genre have been mention in this section frequently, but the cameras you selected are all digital or film cameras that require a housing. And therein lies the rub.
A manufacturer of housings must have a sufficiently large market to justify the expense involved in tooling up, marketing, etc. Thus, he must support a product that has wide acceptance and, perhaps, one that professional photographers will use (in order to lend credibility to any claims of quality, e.g.). Thus, he will go with well-known name brands with professional recognition. Among film cameras Nikon and Canon are unsurpassed in professional recogition, so they are an obvious choice. Among digital cameras, Sony, Nikon, Olympus and Canon are also top choices of the pros. Further, those are amongst the most popular cameras for amatuers and, thus, represent a large enogh market for a housing manufacturer.
These cameras are selected by pros and amatuers, alike, due to the high quality of their lenses and the durability of both camera and lens. Other manufacturers have fine products, but they do not find themselves in the same league for this purpose.
I do not have the sales data needed to quantify my assertions, but I think if you will look at the shelves of any high end camera shop, you will see that my statements make sense, I think.
Hope this helps,
Scorpionfish
P.S.: There is one professional-grade camera that does not have much support in the u/w field: Leica. I own a Leica rangefinder camera and would love to see a reasonable-cost housing made for it. Rangefinder cameras are very fast to focus and very quiet when fired. Many pros use Leica rangefinder cameras still due to the the facts that they are very light, very quiet and very fast to focus. However, housings for them are custom-made and quite dear!