When I order food or drink from a restaurant, I expect to pay for it. I'm sometimes comped things, which come as an unexpected surprise.

I kind of see where you're coming from but I'm not sure I'd take the disappointment on not being comped out on the server - for all you know, management is pretty strict with that kind of thing and the server could get into trouble for doing it.

If you feel strongly about this, give the manager a call. Maybe the server made a bad judgement call, and the manager would like the opportunity to correct it.

For me, I don't see much of a difference between a $450 or a $455 tab, so the inclusion of the soda on the bill probably wouldn't even hit my radar.