Putting the 'suit required' in the job description sounds a tad....childish? Not the word I'm thinking of, but you know.
And I think the job requirements shouldn't really include dress code, since every environment is different, and they might just copy/paste from another posting, or whatever.
I think, if you know it's a professional type place (not a mom'n'pop shop) then you need to either figure out what their dress code is (just ask during a phone screen, if you're going in for a meatspace interview), or just dress to the Nines, and work from there.
I personally don't own a full suit, but I have the pieces of one; slacks/khakis, dress shirts, shoes, and a suit jacket. But it's not tailored to me or anything, just a Wal*Mart special assemblage. And that seemed to work out for the one interview I've worn it to.
Of course, if you should show up in a full suit, and everyone's just wearing jeans and t-shirt/polo, then you can talk about it during the interview, make a comment about 'being overdressed' or something. Interviewers tend to like someone likable and can make/take a joke, at least in my experience.