I certainly know that the service staff makes most of their money from tips but that does not mean that I am obligated to tip. If the service is good (and of course it almost always is with
DCL) I will certainly tip and generally better than most.
I especially have a problem with the concept that I should tip for meals I did not eat. For example, if I dine in my room I'll gladly tip room service but I don't feel any obligation to tip the staff in the dining room for that meal.
I will go on record saying that I agree with you... so there *are* at least two of us!

My stance is based on the definition of "tip", or more appropriately, "gratuity".
The argument "well, tip the dining room servers anyway because if they aren't serving you, they're earning it by serving someone else"..... by definition, that isn't a "tip" anymore, is it? That's more like a donation or a charitable contribution... nothing wrong with it, but don't call it a "tip" that the server "deserves" from someone he never even met.
This thread started out with the question "Do I need to tip anything at all?", and the answer, quite simply, is NO. A "tip", by definition, is a voluntary, at-your-discretion reward for exceptional service. You can tip as little or as much as you wish. To some people, an extra $5 seems like a LOT; others have no problem dropping an extra $20 or $50. I knew a friend who gave all his servers $100 bills.
Tipping is nice... the servers really appreciate it, and they perform their duties with a valid expectation that -- the better service they provide, the better they will be rewarded... Tipping is a gallant, classy thing to do... the "right" thing to do, in most cases.... but it is no way "required" of anybody. If it's "required", than it isn't a TIP/gratuity.
Personally, I would advise prospective/new cruisers to just excersize the pre-paid gratuities option, and not worry about it at all! I love that Disney makes it so easy and hassle-free -- pre-pay your gratuities when you book your cruise, and forget about them (
however, like one person suggested -- double-check your tip sheet to make sure the names on the list match the servers you actually had). If a person can't afford to provide gratuities at the default/suggested levels (ie $528 for an 11-day cruise, or whatever it is), than he/she is probably over-his-head already, and really should be taking a shorter/cheaper cruise.