Disney is a different beast. Even on formal night, you see such a mixed bag. Many people dress more for their dining rotation than anything else. Some families dress up everynight, others not so much.
I remember on Dream, we were dressed and on our way to dinner, when we saw a couple of people (very few) in tuxes. Turns out it was formal night, but there was no real mention of it. Not like on other ships, where the waitstaff tell you the night before, and the CD announces it 50 times during the day.