I guess you don't know what Google is doing? Yes, they're letting people dress more casual, but they're using humanistic psychology as a basis to all their changes. It's a psychology that stimulates self growth that mixes behaviorism and psychoanalysis, it was under the radar for a very long time, but slowly building back up since the 50s. The clothes is maybe 1% of the major changes that effects the person. The main buildings in Los Angeles or New York city have 3 free cafeterias, a gym room, running track, each employee have an extra hour or 2 a day to do what they feel like, if that's taking a nap or what not, + curricular activities including playing with your Wii or 360.
It's not the clothes that isn't killing the productivity, it's the fact they get to step away from the desk, and refresh themselves before coming back to their office.