The quality of the food isn't really a reflection on service staff anyway.
With regard to tipping, the rule of thumb is that if you patronize the dining room, then you should cover the expected gratuities. There are different opinions about that if you don't ever use the dining room, but regardless, there is still the cost-of-service to account for. If you eat dinners at the Windjammer, you can either drop a two or three dollars per person on the table each night, or just rely on the standard gratuity being split between both dining room servers and Windjammer servers. (If you pay close attention, you'll note that the service staff all serve in the Windjammer some of the time.)