Quoth Phone Jockey
Yup, the tip is based on service as well as food order. You did the right thing. I waited table for 2 yrs & it's a tough job, but you gotta at least OCCASIONALLY check on your customers. That's a given.
I forgot to add this to the story. So the next morning, we went back to the buffet (I'm sick of them for the time being!) and were seated in the same spot that we were the previous evening. Our waitress wasn't around, so we decided to go and get our food. On the way to the buffet, the waitress saw us and flagged us down to get our drink order.
I thought it was super cool that she did that. She made sure we had everything that we needed and we made sure that she got a good tip.