...I'm not sure where you get your viewpoint. I shoot advertising images and I do use a 5dmk3, but the files are almost always on the edge of usability...a large proportion of the professional advertising market..
How big is that market? Is it big enough to drive Canon's R&D and marketing strategy? Maybe Canon is willing to let that market go (for a while) to avoid making a costly mistake.
...I guess they could, but I would have thought there's credibility in owning the top end of the market.
I don't disagree. I think it's just a question of what that credibility might be worth...especially during difficult economic times.
My perspective is this: The entire professional market has been shrinking. I don't think anyone can deny that. Some segments may be growing, but even in the growing areas, they are more price sensitive than ever before.
That's not just photography, but just about everywhere. Companies want to get the most for their money and are slashing expenses everywhere they can.
That's reduced the overall market for professional photographers...it's reduced the budgets that are available to hire professional photographers...and it's reduced the resources available to companies like Canon. Those who are at the top of the market may be feeling this less than others as you may have clients who are less price sensitive, but I strongly suspect that for the bulk of the market, photography, like any service, is under intense pressure to hold down costs.
I think, but certainly don't know, that Canon has concentrated on the markets first where they can sell the most at the best profit. I think the 5DIII was perfectly suited to that strategy. The improved autofocus met pent up demand and the improved high ISO performance made it attractive to event and wedding photographers, which is probably the largest remaining pool of professionals out there.
The D800 to me, has always seemed like a fine camera, but it didn't appear to have as clear of a market. I can understand the appeal of advertising shooters but just how large is that market? My sense is that it is concentrated in large cities and I can't believe that the numbers are anywhere close to the numbers of wedding and event photographers. Professional landscape photographers are an even tinier subset of the professional base.
So, my premise is simply this: I think Canon went first for the largest market with the 5DIII. They actually "over-delivered" based on what people were demanding. (Go back and read threads from when the 5DIII first came out and see how many wedding photographers were ecstatic over the ISO performance and how many others were stunned that Canon would put almost the same autofocus as the 1DX in the 5DIII.)
The high megapixel market is a niche market. For those who need it, it is critically important. I understand that. I just don't know how many people need it.
So, this all goes back to my main premise, which is that the most cost effective approach for Canon would be to take an existing model (either the 1DX or the 5DIII) and produce a High Definition or HD version. That would allow them to maximize some production efficiencies while meeting the more narrow needs of those who want or need a higher definition body.
Long post I know, but trying to explain my reasoning. If you can show me where I am wrong, please do. You know the market better than I do and perhaps I'm totally off base, but so far, no one has been able to show me that.