Times change, and fashion faster than most. That's not really a bad thing. A national dressing-down might even symbolize a desire not to be bound by dictates of formality or convention but to express our true selves. Whether it's more than an outward show is certainly debatable, but it's a noble thought. When we perpetually dress down, nothing seems quite as special any more.
Class is little different from going to the mall or hanging out around the dorm.
Church is no different, attire-wise, than a concert, which isn't really different than listening to Handel on a CD in the living room. Some things, it may be argued, should remain special, and dress is one way of showing that. Just as the formal hymns and structured liturgy of worship lend an air of dignity to a Catholic Mass, so should dress indicate a more dignified air at certain events. Now, just as there are few who would steadfastly argue that a Catholic is more worshipful than a person at Great Commission Fellowship simply because of the greater pomp of the service, few would be quick to argue that people can't appreciate a concert because they aren't dressed to the nines. But there is something to be said for dressing up, and there is something to be said for keeping at least one event on campus more formal than the usual routine.