I'm not a designer either, but I can see their point of view: they're being paid to make a website internally consistent, and if they can't style scrollbars, then either they're stuck with a bland, vapid style that looks reasonable across all platforms, or they make something that's cool and awesome and makes their clients happy right up until the first scroll-bar appears, at which point it looks ridiculous (in particular, think about a <textarea> where you can style the border to match all your other form-fields, but not the scroll-bar, so you wind up with two visual styles pressed right up against one another). Being responsible for something you can't really control is frustrating for anyone, so I have a measure of sympathy for the designers who want stylable scrollbars.