Did Alaska 6/03 on Celebrity. Table was 4 couples, 3 wore tuxes (one rented, VERY poor fit). Last couple wore nothing but wash pants and polo shirts w/ sweaters to dinner EVERY nite, casual, informal or formal and they were experienced cruisers (>10).
Use of tuxes vs. suits will be somewhat dependent on cruise line and general cost of cruise. More upscale lines (generally more costly) will have more tuxes. These pax tend to own their own.