One thing that I've noticed with Canon DSLR camera is they will disable or limit autofocus when the lens' maximum aperture is narrower than certain values, which are specified in my answer to What apertures are required to enable autofocus, including cross-type or high-precision focusing, on Canon DSLR cameras? Note that Nikon cameras are also typically limited to f/5.6 except for models featuring the latest revision of the Multi-CAM 3500 AF system as in the D4 and D800.
As far as I am aware, Olympus and Pentax do not have these limitations, even if autofocus may be slow or unreliable beyond f/5.6. (Sony/Minolta requires at least f/6.3, with one exception for a 500mm f/8 autofocus mirror lens, and the Alpha 850 and 900 have a center AF point with high precision at f/2.8.) For example, on Pentax, 9 of the 11 points are cross-type and remain so at all apertures. The Pentax AF system has been reported to work at f/8 and beyond, though extremely slowly. Olympus Four Thirds cameras will continue to attempt to focus below f/5.6 as well. Why do Canon and Nikon choose to limit AF functionality instead of attempting to focus with reduced performance beyond the above cutoffs?