The era of casual dress crept up on us slowly, but now every organization this side of Wall Street seems to have taken up the khaki banner. (And even Wall Street is apparently not immune to the trend.)
Making a positive statement is never more important than when you walk into the room for a job interview. First impressions are lasting, and a job interview is not the time to cut corners on your professional image.
There is a lingering perception that the type of clothing a person wears has some impact on their performance at their job. As one completely opposed to the wearing of business suits, I find the total lack of discussion in this area to be fairly discouraging.