For me it comes down to taste and respect for norms. I've worked in hacking environments where as long as you've got clothes on and showered yesterday you're fine. I also worked at Accenture where the dress code was "smart casual" which meant "tidy, neat, conservative." I prefer hackers but Accenture paid better.

These days I work at a creative agency and although there's no dress code I have to collaborate with co-workers and rich clients. If I wore my most comfortable frayed, discolored, "liberal" clothes I'd feel lots more creative but would fear for my job. I'm not Michelangelo or a scientist, I'm just building web sites. But there are serious artists here who work with me and they dress "tidy, neat, liberal." When they wear shorts and sandals, it looks good. The reason is, they spend their money on beautiful clothes. There's a conscious way to do progressive and then there's a poor, just rolled out of bed, I don't care way.