With more searching I found the definition of "Americast":
"Americast® brand engineered material is a composition of porcelain bonded to enameling grade metal, bonded to a patented structural composite."
It seems that it's porcelain on a "thin" metal tub which is reinforced by a structural composite. Does this sound about right to you pros?
EDIT: Found the weight of the tub which is 190 lbs. (RE-EDIT: See post below for tub weight.)
Since I answered my own questions and it appears to be a good and sturdy tub, I think I'll go with this tub.
Thanks for looking anyway,