Let me restate. Mobil1 does not make 5w20 in their extended performance the way I understand it. Their 5000 mile oil is petroleum oil: their 7500 mi oil is a blend. I don't think there is a syn blend oil that is GRP IV. Correct me if I'm wrong. Only M1 EP is a group IV.
The question was asked why are they not making an ep 5w20? They make it in the 7500 mile oil only. Also Amsoil makes an xl 5w20 which is a 7500 or 6month oil. Thus I said to the question, I don't think they want to spend the money to develop a group IV 5w20 for whatever reason.
Your statement G-ManII was correct that all Mobil 1 is group IV oil until Mobil came out with 5000 mile, 7500mile and then Mobil15000 EP. Now I believe only EP is a true PAO Group IV oil.