Mobil one and pennzoil I think had a big court case a while back about what can be called "synthetic". Mobil lost, and the case determined that hydrocracked dino oils are also "Synthetic." So now Mobil has taken to the addage, "if you can't beat'em, Join'em" They produce hydrocracked dino oils that are "synthetic" by the governments standards.
Also, I read an article from Amsoil a while back that said 0w-20 oil was a way for automakers to reduce emmisions, and increase fuel economy. It said that taxes are based on average fuel economy of their entire lineup. So the lower any single car is, the lower their taxes overall.
Amsoil 0w-30 is honestly the best oil money can buy. I run it exclusively in everything I own. Their oils have always tested better than Mobil1 in every category.
Also, the 0w is the cold starting viscosity. the 2nd # is the one that you should really be concerned about, unless you live in extremely cold environments.