Nolan had wanted to wear a suit since becoming the Niners coach to honor his father but ran afoul of the NFL's licensing rules. You can't have people just wearing clothes all willy nilly without having some sort of logo on it after all. After some discussion last year, Nolan was allowed to wear it for two games last season (and looked pretty darn sharp too we might add) but after an internet campaign was waged, the NFL acquiesced and will allow him to wear the suits-- designed by Reebok of course with their logo tastefully splashed somewhere.
Niners fans were actually planning on staging a protest at the home opener by wearing suits. Somehow, we don't see Raiders fans doing the same thing.