Your absolutely right. I've been in many formal restaurants where jeans and shorts are worn. Most of the power steak houses, where I have gone I see both the business dress and the dress down attire, and I have dressed both ways myself. It's really no big deal anymore. Look at how people use to dress when flying, it was a formal affair. No more.
With the cruise ships having more entertainment activities, such as rock climbing, ice skating, etc. who wants to do a day of those activities, than go down and get all dressed up. Things do change..