No, it just means that if your lens largest aperture is smaller than f/5.6 (next step is f/8 typically) it can't autofocus. Focusing is always made at largest aperture, the lens is stopped down to the target aperture when taking the picture.It seems what torger implies really IS the point.
Lenses don't have as small as f/8 natively, but with teleconverters you get it, 1.4x adds one stop, 2x two. So if your camera cannot do f/8 autofocus you cannot get autofocus with a 2x teleconverter on an f/4 lens or 1.4x on an f/5.6 lens, which can be a limitation for especially wildlife photography. 2x on 500/4 to get 1000/8 with autofocus can be a nice option to have. Or on the low end 400/5.6 => 560/8.
I should think there would be a good number of sports, wildlife, et c., professionals who have long, relatively-fast lenses, but occasionally find themselves in a situation where they need that extra reach. Putting a 2x converter on an f:4 lens brings one to that point and, with depth-of-field being so narrow at 800, 1000 or 1200mm, that autofucus is virtually essential, particularly given that the viewfinder image at f:8 is not going to be bright.
It seems there would be even more photographers who'd be likely buyers for this camera that possess lenses of modest apertures, but sometimes find themselves in situations where they'd like that 1.4 or 2x "boost", as well as those who don't always carry their big glass around.
I certainly hope that Canon will fix the "Achilles heel" for what otherwise appears to be a stellar camera. Autofocusing at f:8, even if only in the center spot, has been a given for 1D series users for a decade now. Taking it back seems such a step in the wrong direction and gives us one less reason why these bodies are our first choice.