Well if that is the case, that all tips are pooled and it does not affect service, then I see no reason to tip. Don't get me wrong, I think these people deserve all they get but lets take a closer look here.
My tip does not go to the person I give it to. This means that what we really have is another surrcharge by the cruise lines that is used to suplement the income of the service staff because the cruise lines refuse to pay a decent wage. It is no longer a tip.
I am not against tipping, and in fact are quite generous in my own tips. I am however against add on surcharges. Do you remember the stink that was raised when cruise lines removed the port charges to make their cruises look cheaper, but added them on when you booked? We have the same thing here. Lets call it what it is, a service fee.