I've noticed a distinct downward trend with regard to dress formality over the years, at least here in the US, but it appears to be spreading worldwide. "Formal" now seems to mean that collared shirt should be worn, with the tie and jacket (coat) being optional. I went to a formal dinner a couple of years ago and saw quite a few men wearing a tux jacket with a t-shirt, jeans and sneakers/trainers. The level of casual dress appears to be determined by how many holes are allowed in your jeans.

I see similar discussions on cruise forums about what to wear for formal nights. Passengers complain about having to dress up and wear a tie, asking if a polo shirt and jeans are acceptable, preferably worn without a coat. I'm surprised by the number who post saying they don't own a tie, let alone a jacket.