It sounds like you were just trying to find some way to justify in your mind a low tip and pay less. That or it's disappointment from a misplaced expectation. If you order it, expect to pay for it. End of story.

Sometimes I'm OFFERED a free drink/dessert/appetizer but I don't punish the waiter whenever it doesn't happen.

Is soda at any bar or restaurant overpriced? Absolutely but you already knew that walking in the door.