I personally don't really believe that. It depends on which amino acids are in which type of particular protein. There are 22 amino acids I believe.
Anyway, Whey is usually reguarded as the best for weightlifting because it absorbs into the bloodstream within 30 minutes.
The FDA reccomends 25g of soy protein a day to help fight heart disease and certain cancers. I love soy protein...
But theres so many different types of proteins. I was reading about it yesterday in a chemistry book, because there are so many different amino acids, the structural combinations of proteins are virtually limitless.