It's quite simple - service charge of 15%-20% IS the tip. If the hotel doesn't pass it back to the delivery person, then that's hardly my problem.

As long as I see that on the bill, I put a line through the 'tip' space and just sign for the total. I've actually had delivery people tell me that "the tip is already on the bill, Sir", which I thought was a nice, honest gesture.

Then that pesky delivery charge is just something they put there because "they can". Just like the $1.50 local/toll free phone charges and $5 cans of mini-bar soda.