[phoenixy1]

This rule of thumb, when used correctly, is supposed to refer to womens' dress straight sizes. As in, for an average height woman, losing 10 lbs is roughly equivalent to going from a size 8 to a size 6. It doesn't refer to clothing that is sized as "medium", "large", etc. (I did not read the article; it seems from the quote that the author was using this rule of thumb inappropriately and out of context.)