I noticed the price difference, too. I asked a friend who has been in the auto industry for 30 years and he asked me "Do you think there is a profit incentive to invest in product designs, development, testing, etc., of two brake rotors [in my case] for the same vehicle?"
There may be an element of marketing (brand recognition, etc.) or price-point access.
I ordered the Ford rotors and they are cast with "Bosch". I haven't seen the Motorcraft, so I don't know what is cast on them, but I suspect Bosch (maybe someone can chime-in). It is odd that the Ford were less expensive than the Motorcraft (parts guy said he hadn't seen that before).
Ultimately, I went with the Ford rotors and Wagner SevereDuty Brake Pads and have been satisfied with the setup. I do a fair amount of mountain driving and this is a great improvement. The pads take a couple seconds to warm-up, but once warm, they bite hard and don't fade (better than OEM and ThermoQuiet, IMO). I haven't noticed abnormal rotor wear.