you are right = apparently this newest attack of norovirus is a very virulent strain. The symptoms are pretty rought from what I hear.
I have had noro (not on a cruie ship) and it is not fun.
By the way - my mom's senior center had an outbreak of Noro this last week,and almost 1/2 the residents got it. On most cruise ships it is rare if it gets to 10% of the population onboard.