On the cruises I have been on -at the most- maybe 30% of the men wore tuxes-and this was on HAL-much less then that on Carnival and Royal Caribbean. In 11 cruises hubby has always worn a suit.
There's actually a very interesting dyanmic here. On lines that attract an older crowd, like Holland America Lines, you'll see a high percentage of men wearing dark business suits because most of the men own suits that they wore to work before they retired still fit. On lines that attract a younger crowd, you will see more tuxedos and dinner jackets because many businesses now have a "business casual" standard of dress even for professional staff. Those who don't own (or have occasions to wear) business suts tend to rent formalwear because it's considerably less expnesive to rent a tuxedo than to buy a reasonably good business suit.