While it is true that UV filters are rarely necessary, there is another benefit of using them besides as a protector. They keep you from having to clean the lens surface as often, or sometimes, ever. If you clean the lens perfectly (or when the lens is brand-new) and then attach a good-quality filter you are effectively "sealing" the lens surface and any subsequent cleanings are of the much cheaper filter and do not risk damaging or swirling the lens coatings. Hoya Pro1 and their sisters Marumi Super DHG are of moderate cost and will not affect IQ unless it's a situation where they could introduce some flare, and that's really rare if you're using the hood.
I am not as adamant about always using them as I used to be, but I do still keep them on my "work-horse" DA*'s and my long Sigma and have never noticed any ill-effects whatsoever. This will especially appeal to people like me who are kinda anal about their equipment and to the people who buy used lenses from us as they end up with lenses that are in perfect condition.