Making blanket statements like this is rather silly. It's entirely dependent on your field and the programs. I've also been to three interview sessions so far and not a single person has worn a suit, and the one person I saw with a tie consistently looked out of place compared to everyone else. Jeans have also been worn by at least half of the people. Go with what you know about your own field, or better yet, simply ask your host or the people arranging your visit, it won't hurt, and it will give you better advice than agonizing over conflicting responses here.
