I'd expect people to turn up looking quite smart, but wouldn't demand a suit.
But impressing at an interview is a layered thing anyway, it's the sum of a number of parts and if wearing a suit is going to give you a little bit extra, why not wear one?
Not wearing one to make a point is certainly going to lose you the job.
Personally I'll always wear a suit to an interview, it can only help me and costs me nothing (assuming I already own a suit). So what if one person doing the interview is the type of person who is impressed by a suit, I'm not getting the job for his benefit, it's for mine.