[Zeke]

The reason a gratuity is added on a large group bill in a private room or otherwise in a restaurant is because of the extra staff it takes to serve the guests. That doesn't mean the person making the reservations or taking care of the bill shouldn't seek out the lead server and tip them if all was good or better. Of course, this would not apply to a banquet where you bought in individually unless you feel compelled.

I think the "service charge" for room service is to differentiate from the restaurant or coffee shop prices. True, the room service menu may not even be the same or same prices, but nevertheless, if there wasn't a "penalty," everyone would stay in their room. Again, it takes extra staff to bring, serve and remove the service cart.

That has nothing to do with the person bringing the food. If they are polite, quick and efficient, they deserve to be treated as such with a tip. If there is something wrong with the food or service, it should be explained to the staff, not just stiffed.

The tip rate should be commensurate with the already in place charges. The server will keep the tip whereas the charge will be kept by the hotel, some of it may be pooled to the staff.
So, if the server makes 2 trips to your room, I should think 5% is plenty as opposed to 15-20% in the dining room for continuous service. However, 5% of a $20 item for a single occupant would be a dollar. One has to be prudent here.