I don't think you're getting it. Even though the tip is for your dinner servers, it covers all meals (breakfast, lunch and dinner). Even you don't get your specific server in Cabanas (for example) for breakfast, or serving you your hot dog on the pool deck, the "dinner" servers also work those locations. Your tip covers all meals. Are you planning on not eating anywhere onboard?
I don't agree with your premise here. If that is the case then DCL should just charge the the tips as part of our cruise price and if someone goes above and beyond you give them a little extra at the time of the service. The best server we had on our last cruise was a from out embarkation lunch. Whenever we saw him throughout the cruise he found a way to help us out. He definitely didn't benefit from the tip our servers got. I have said on another tipping thread that maybe DCL should have an opt out option for the mdr for those families that have no intention of going. Not sure there is a good answer here.
I am with the op, something just seems off when you tip for a service you never received. I thought part of our cruise fare goes towards paying for the buffets and the quick serve food on deck, there is very little cm interaction in those venues. Lunch in the mdr however is different, you actually do get table service there.