The problem with selling pants by waist measurements is that women's pants rarely actually sit at the waist. I prefer a waistband at or below my bellybutton, which is significantly lower than my natural waist. My waist may measure 28", but do I want a 28" waistband? Nope, I want one with a waistband about 30"-32".
Oddly enough, though, some stores here DO sell women's jeans by waist size, and I do fit a 28-29. I don't get that.