I was asked the other day if I ever wear jeans. The answer is no, for several reasons. I wear cargoes and docker-style pants because I have found that the cargoes are more useful (extra pockets)they look dressier and an added benefit of being more comfortable. But there is more to it. People judge you based on your appearance. The part that is perhaps most important is that people perceive the value of your work to be greater (and therefore your importance to the company) when you are well dressed.
For example, Beach Bum Joe comes in flip-flops and Hawaiian shirts and puts out 100 widgets a day. You, dressed in slacks and wingtips puts out 90 widgets a day. From an empirical standpoint, Beach Bum Joe is of greater value to he company, but he will not be perceived as such. And until humans are no longer in charge of the decisions that perception will matter greatly. Especially since most of what we do in our modern economy cannot be quantified like widgets can.
So I have taken to trying to look nicer, wearing polos and full buttoned shirts. At the moment that is all that is required to be better dressed than most others in the office, but if this article is correct it might not be enough before long.