Company dress policies are to set a 'minimum' level of acceptable attire. I've never heard of a policy saying "suits are not appropriat attire" (accept where they are, of course... warehouse, construction, where uniform is required, etc.)

Our company (California companies are very concerned about sexual harassment and hostile environment lawsuits) is very specific about what can be worn by whom, and when. But those are always minimums. You are always allowed to dress nicer than the stipulated code.