Just from observation, so many people come in and stay for just a few minutes or take their coffee to go that it's kind of a nice equilibrium. It's rare that you'll find a coffee shop in Pittsburgh to 100% capacity (except perhaps Sunday afternoon or evening in the fall and spring). Electricity costs nothing. If anything, having people in your coffee shop serves as a kind of advertisement that it is a place people want to be for whatever reason -- the coffee is good or they just feel comfortable there.
As fantastic as Manhattan is, there are two reasons why I wouldn't want to live there: too many tourists and too few coffee shops. The best I could find in the upper west side was Cosi, a chain. The best I could find around Soho was some piece that closed earlier than shops in Pittsburgh. And the best I could find in the Upper East Side closed a couple years ago. Pittsburgh, baby. Awesome place to live if you love the coffee shops.