This also plays out in the overall upgrade strategy that Canon appears to be following. One area you see that is the AF systems chosen for the non-1-series bodies, where improvements are slow to 'trickle down' the lines.
I think body strategy regarding AF is one of the strong points of Nikon vs. Canon. Nikon has more of a gradient for AF performance across it's line, with each body (more or less) inheriting the AF system of the next higher model's previous generation. With Canon there are large steps in AF performance. Even the 7D with it's highly regarded AF system is only comparable to the 1D2 maybe the 1D2N (from what I've read, I haven't used either).