It's not peculiar once you recall the genesis of the product. The Mobil 1 AFE oils were originally just Mobil 1 oils in the 0W-20 and 0W-30 grades. Mobil recommended them for any application that called for 5W-20 and 0W-30 respectively. In order to make them stand out a bit more, they added the green caps and alternative label and "Advanced Fuel Economy" tag line on the label, the oil itself remained unchanged.
This is different from the EP and High Mileage oils, which are actually separate families of formulations.