JRob,
Those are good points. I know that I've seen one high end shampoo--can't remember the name---but it came in a kit with several different versions of the shampoo and a water testing kit. It's intended for the executive that travels the world. It called for the user to first use the testing strips to determine the hardness and quality of the water. Then the user would use the appropriate shampoo to 'match' the water quality. It makes sense--the hardness and chemicals in the water are a big factor in how effective a shampoo is. I think that's why people will try a shampoo that someone else loves and then not get the same results---the water quality is different and it causes different results with the shampoo.
John