Ford is probably just picking up a few dollars for shilling BP gas. As far as GM using Mobil 1 for factory fill and recommended replacement, here goes:
By using Mobil 1 in the Corvette that allowed them to get rid of the oil cooler since M1 will hold its viscosity better when it gets hot.
In the rear-drive Cadillac Northstars, there are special valve lifters which require an oil that maintains a very stable viscosity over time, hence again Mobil 1 is recommended.
A lot of garden variety 5w-30 dino oils are effectively functioning as a 20-weight after about 2000 miles.