I understand where the OP is coming from on this one. When you've spent that much, especially once you already have the bill, adding to it for a non-alcoholic drink seems a bit cheap.

On another thread, I posted about placing a take-out order at the bar at a location, and being asked if I wanted anything to drink while I was waiting. I ordered a Diet Coke, and was a bit annoyed that I was charged for it, in part because IME, most bartenders will comp a soft drink while you are waiting for take-out.

To some extent, restaurants must balance keeping customers happy (comping soft drinks when people are finished with their alcoholic drink or waiting for take-out) and making a profit (soft drinks tend to cost the establishment pennies, but are marked up substantially).