Dude, I found this which made interesting reading:
http://www.atlargenutrition.com/wheyprotein.php
"Protein supplement ads and articles frequently cite Biological Value (BV) numbers (e.g., 104 and sometimes even higher) for whey as evidence for its superiority; however, these BV values were derived from studies on hair- and feather-covered animals that require more of the sulfur-containing amino acids that whey is rich in. These results do NOT apply to humans."
As with everything, pinch of salt is always to hand but I did not know the above and whilst it's supposition, it's interesting nonetheless.