Probably all of the photographers above have worked hard for many years refining their art. As you know, Sony have not been around for that many years, so these people will not have started off using Alpha mount. It's the hardest thing in the world to give up a system that one has got used to, particularly when it includes expensive and cherished lenses. Therefore, there lies a great deal of inertia that tends to be self perpetuating as the herd instinct takes over. Everyone wants to be like Simon King so they go out and buy Canon because he's good, therefore what he uses must be good, right? They put up with the same foibles and flaws that the experts have got used to instead of trying different cameras out before buying and deciding on what suits them best.
Canon sensors are good at high iso (getting to be a one trick pony here), but they aren't the sharpest on the block and you don't have image stabilised macro capability. The latter is why Canon users carry tripods or monopods when shooting butterflies. I get pixel sharp pictures without such encumbrances.
Nikon sensors, particularly their latest ones, are probably the best in their category, and the cameras are well built, but Nikon cameras cost 50% more than the competition, and the menu system is cludgy and unintuitive. There is an image stabilised Nikon macro lens but it costs the earth.
Of the rest, only Sony is expanding its system, and increasing its sales. It is true that Sony sensors are known to suffer more noise than Canikon, but they are sharper and more detailed in good light, and the noise is only equivalent to about half a stop. The A700 and A900 'serious' models are weather sealed, gimmick free, having superb handling and intuitive menu systems.
And, not to be sneezed at, there is a great deal of early Minolta glass around on the s/h market that has colour quality that is unmatched by Canikon or anyone else.
Incidently, Matthew Oates uses Alpha mount.
BTW, who or what is Linhof? It sounds like a subversive German organisation.