A primary reason for using vinyl windows is expense. Any builder wanting to use such windows is likely looking for a way to save a few bucks on the overall expense. It's not necessariy a bad thing, as the particular manufacturer may provide a quality guarentee of sorts. However, aluminum clad windows are a better window. More expensive, they are a more solid choice, and unlikely to be as affected by UV rays as the vinyl ones are. In short, if you have a few extra dollars, and want quality windows, go for aluminum windows, double glazed.