This all goes back to a few different things:
1. Big Pharma doesn't like the availability and usefulness of many of the "joint" supplements, because many of them DO work, and this eats into their sales. There will be more studies coming out saying similar things. Follow the money trail and see where it leads.
2. Scientific study design is really ridiculous. Lately I've been reading this guy's blog (http://evidencebasedfitness.blogspot.com/
) and it's been extremely interesting to watch him shred study after study for incredibly poor design, poor use of statistics, and just overall goofiness.
Don't think, for one minute, that many (even most) scientists are well versed in the design of studies, or even in the scientific method.
3. Multiple joint supplements seem to be synergistic. For example, one brand of glucosamine didn't do anything for my knee aches at all, but when I switched to a glucosamine, chondroiten and MSM blend from the same company, my knees got immediately happier.