Qualify what you mean by poorer service. Just because the service is different doesn't mean that it's worse. I'd take a waitress that was curt and left after I'd placed my order over one that asks me if I need anything every 10 minutes.
I tip well at the bars I frequent because stopping by every 10 minutes means I always have another beer sitting in front of me right before I finish the one I already have.
I don't enjoy fighting for the bartenders attention with the attractive person on the other end of the bar; tipping is how I level that playing field.
