NAND, the type most likely used inside the upcoming 1D X, is very cheap (and has never been cheaper) and is of a slower spec than what is found inside today's desktop computers. I don't think memory cost is the primary deciding factor for these decisions anymore.
Again, regardless of the chip price the labor and logistics of getting those chips on a micro board such as is found in cameras is more expensive. We're talking relative here and compared to the list price of the 5D3 and 1D X really insignificant but they will save a nickel per unit if they can even if it diminishes the performance if they think they can get away with it and this goes for all the manufacturers, not just Canon. A good example would be the plastic mounts on the lower end lenses. Just how much are they saving per unit, a few cents? Insignificant even on the cheapest lens, the nifty fifty at $110 or whatever it costs now. Nikon's 18-105 VR has a plastic mount and though it is included in kits if you buy it separately it is $400.