Mike you have received some wrong information about formal night. If you plan on eating in any of the main dining rooms then the dress code for the evening is formal. If you plan on eating at the buffet or ordering room service then you do not need to get dressed up.
They wouldn't throw you out of the dining room if you wore a sport shirt and slacks on formal nights, but probably ever other man would be wearing either a tux or a dark suit. I dislike getting dressed up, but I reluctantly do so.