Interesting point, Isabel, on both placebo & older dogs with exercise.
When I'm talking about the 'placebo effect,' I think about it more on the part of researchers & doctors, than individual owners. Seeing it work or not working on one, several, or even 10 dogs of various ages/health just would not give a large enough sample population to have an idea of any drug's effect. There are too many variables involved.
From what I understand, MSM & Glucosomine have been used for at least a decade in the treatment of horses. At least, that's how long my mom has talked about using it. So who knows how long it's been around? It seems that what starts out in horses, moves on to canines, and then to human usage. Remember the packaging of hoof treatment for nail care?
As far as older dogs getting more exercise, I"m really for it. I see too many getting really sedentary, putting on weight, and not having any human stimulation. Just like us in our modern world. ;)
Use it, or lose it :)