I am pretty sure i referred to your case, or a similar one, in an article I wrote last year about people being denied boarding. it does happen and there is no guarantee you will get a refund.
I think most people think that if the cruise line cancels your cruise they owe you the money, but unfortunately (whether they do or not0 it is not their policy to give it to you.
It you get any compensation at all consider yourself lucky.
It appears that the number of "sick" cruises has gone down dramatically in the last few years as far as I can tell. I certainly have heard far less about them recently.