A lot of that pricing started out as a result of binning.

Making CPUs is really hard, especially with larger die sizes, so you're likely to end up with defects in some of the chips you make. But since the defect might only affect some of the cores on the chip, you can just disable those cores and sell it is a 4 core chip instead of an 8 core.

Eventually the manufacturing process gets better and better and you have fewer and fewer chips with actual defects. But you don't want to cannibalize sales of your higher end chips, so you just artificially disable cores on some chips to keep your market segmentation intact.

They would also do similar things with CPU clocks as what you mentioned for RAM- where they would test each CPU and the more stable ones were sold as higher speed chips, and the less stable ones as lower speed.