MODS - could you please delete my previous post - I tried to edit it but I missed the deadline. What I meant to say was:
It's interesting that the Amsoil FAQ says "The State of California has specific requirements strictly enforcing the OEM’s viscosity requirements for their specification", whereas the California law itself is broader than just viscosity: "Any automatic transmission fluid sold without limitation as to type of transmission for which it is intended, shall meet all automotive manufacturers' recommended requirements" and "Automatic transmission fluids that are intended for use only in certain transmissions, as disclosed on the label of its container, shall meet the latest automotive manufacturers' recommended requirements for those transmissions".
It looks to me that if you say a fluid is for use in a GM transmission, regardless of whether it's just for GM transmissions or for GM transmissions and others, it MUST comply with GM's "recommended requirements for those transmissions". GM's recommendations are "use only Dexron VI". That means the fluid has to be "Dexron VI" fluid, not merely "suitable use where Dexron VI is called for".
I'm sure Whitewolf would make the point here that Dexron VI is more than a viscosity spec, and that to be Dexron VI fluid it has to pass GM's Dex VI test sequence and get a license number.
By the way, I'm not being critical of GM, California or Amsoil. I think the law was drafted to achieve a goal around clarity for consumers and so there will be lots of opportunities for manufacturers to try to find ways to comply with it without actually going through the full and very expensive certification process. It's unlikely that the consumers will be worse off than they were before as a result of the new law.