I might as well throw in my 2 cents being in the professional circle... There are different groups of "professional" photographers... The people who has been in the market for years and has a want/need for large cameras such as the 1Ds and can justify it on a daily basis, and professionals who are happy where they are and while they would love to have the accounts and budget to afford the best, they have to make due with what they got. I personally fall in the second range where I'm not making the $$ i could in other areas and if I had this and that, however at this stage in the game, my wife would kill me if I plunked down $4000-7000 down on a 1d or 1ds... However the 7D/5D are more in my budget so I make due. Believe it or not, the groups of people who can afford the 1d series cameras are small which high potential profit margins... Newspaper agencies, advertising agencies, top tier photographers, etc... and to be honest, like the rich who can afford high end cars, they are built better so they typically last longer and owners hang on to them longer than people who buy fords or hyundais or kias... You buy a 1d series and while it costs a lot more, they are built like tanks, have excellent ergonomics and to be honest, unless you need the latest and greatest... There are several pro's getting along just fine with older 1d series cameras because they dont NEED to upgrade as quickly unless they wear out their camera or are going broke. Typically if you can afford the 1d cameras you usually have a large enough investment in canon and likewise with nikons D3/4 series cameras and their investment in Nikons that I dont see much of a flux in that top tier. However it is the mid range pro's 7Ds,5Ds,D300's,D700's where you see all the movement and why these cameras sell so quickly vs the top cameras.
If Canon really wanted the 1D's to fly off the shelves they would market them to the mid range to amateur photographers and price accordingly, however they dont. They know what market share they are going after with that range and they are comfortable marketing to those photographers.
Lastly, dont forget the economy right now... few people can justify spending that money on such an expensive camera... Even agencies are tightening their belts and holding off upgrades, so I wouldn't start getting paranoid just yet.