The Kohler name isn't what it used to be...
Make sure to compare apples to apples. My guess is that each of these companies make acrylic, cast iron, and probably other types of tubs. A cast iron tub will last decades and still look good unless you use harsh abrasives (cleanser) on it. It is harder for anything else to look as good for that long.
So, what material are you interested in? One thing to check out is the relative thicknesses of the material.