Another possibility is a difference is glucosamine formulations

A recent study of 40 "complementary and alternative medicines for the treatment of rheumatoid arthritis, osteoarthritis and fibromyalgia" showed glucosamine HCl (hydrochloride) was ineffective in relieving osteoarthritis. However, the same study showed glucosamine sulphate *is* effective.

Read the study here: http://www.arc.org.uk/news/pressrele...reness/CAM.asp There's a link in the bottom of that page to the full report.