They do use PAO, but only a small amount and it's used more as an additive to keep the oil viscous stable.
See here's the problem, and i don't know the specifics so bear with me here, but the story as i understand it goes something like this. Sometime in the 90's castrol came out with an oil claming to be synthetic called syntec that was cheaper than M1 synthetic. Appearantly castrol was buying there oil from shell from there group III base stock. Exxon mobil sued castrol for falsely labeling there product as synthetic (synthetic being man made or Group IV and V, not from petroleum). They lost the case and the court ruled that the term "synthetic" was a marketing term and nothing more. Therefore now here in the US, manufacturers throw around the term synthetic all the time while using group III base oils.
As far as what mobil 1 uses now, i could be wrong but i believe they switched to mostly using group III base with a small mix of PAO to compete with the other brands who are marketing synthetics. However they were previously using PAO as there base stock, with a small mix of group III and additives mixed in but i could be wrong.
2007 Mazda 3 hatch
1972 Porsche 914 roller with plenty of holes to fix