I have noticed that what happens aboard ship is very dependant on the crew. Different cruise or activity directors have different seminars, classes and games. There seems to be no corporate edict that says each cruise shall contain: trivia contest, dance classes... It is just what the event staff aboard your ship cook up in their heads.
I recall on Norway that dance classes were offered quite often on their 7 day cruises, and I remember a few classes on our Pacific Princess 7 day, and line dancing was the only thing I saw on Westerdam. That could change when some of the crew changes in their regular rotation.