Neuro... -realistically, what physical/manufacturing cost savings would leaving out a reasonable auto-focus system provide? I'm thinking in terms of raw material it's next to no extra costs, and in terms of manufacturing techniques, it's nominal for them to make the extra effort
Handicapping the 5DIII AF isn't a production cost-saving measure, it's a marketing strategy to drive differentiation. As whatta correctly points out, including AFMA in the 60D would have been essentially free (there's no hardware component, and the algorithm was already done), but they chose not to do that. Fundamentally, they need to have market separation between the 1D X and the 5DIII (and between any other lines, as well), and AF performance is one way to do that - it's one that Canon has a long history of using. IMO, especially if Canon puts a >21 MP sensor in the 5DIII, they'll need to have other ways to differentiate it more strongly from the 1D X than if they use the same 18 MP sensor as the 1D X.
Think of features as a set of sliders like you see in financial/loan calculators, and set has to sum to a fixed final ranking. So, the 1-series has all the sliders pegged to the right-hand side (100%), and the xxxxD has them all pegged to the left (0%). For models in between, think of xxxD at 25%, xxD at 50%, and xD at 75%. Compare 7D to 5DII - the 7D has sensor size and MP bumped down (APS-C is not as good as FF, 18 vs. 21 MP), so the frame rate and AF sliders are bumped up, as is weather sealing. If the 5DIII has FF, higher MP, equivalent AF as 7D, 5 fps, better sealing, etc., it becomes 90%, not 75%, and that's too close to the 1D X. In other words, the better the sensor in the 5DIII, the worse (relatively) the other features. For example, a 5DIII with a 28 MP FF sensor with the ISO improvements approaching the 1D X would likely mean using the exact same AF as the 5DII, lower FPS and perhaps even reduced build quality/sealing. These trade-offs aren't necessarily determined by costs, but rather by marketing strategy.
AF type? Nikon seems to have a better AF approach
True - Nikon doesn't differentiate the pro line from the semi-pro line with AF. Instead, they differentiate based on sensor resolution. You can get 'pro' AF short of the D3x, but then you're limited to 16 MP APS-C or 12 MP FF. If you want high MP and
pro AF, you're stuck with the $8K D3x.