I don't use Amsoil, but I see on their website (Dead Link Removed):
"AMSOIL 100% 5W-30 Motor Oil is designed to provide maximum benefits in gasoline-fueled engines. It meets or exceeds the following specifications:
API SH-SJ-CF
Chrysler MS 6395 H
Ford WSS M2C-153G
GM 4718-M
VW 500.00, 501.01 and 505.00
Energy Conserving II
ILSAC GF-1, GF-2
Mercedes-Benz AG 226.1"
I don't know the law all too well, but I am guessing that a company can't say it is API certified unless it really is.
Also, maybe I'm missing something, which wouldn't be a first...