Ron if two hundred or more people are sick on a ship chances are 90% of them got it on the ship. I'm sure a passenger probably brought it on to the ship from shore originally.
FYI - Norwalk is not just a little stomach ache, you are violently ill. My daughter spent all but one day in our cabin. She unlike others listened to the doctor so she would not spread the disease to others.
As for compensation I did not ask for anything, RCCL offered it up to my daughter and myself so I did not turn it down. I'm not sure why they gave compensation to all of us who were traveling in our party because the illness did not spoil the others trip. Our friends who were in another cabin were not even quarantined. No one asked for compensation RCCL was just very generous!