this is the Point. You do not buy breakfast for 13 EUR but you buy a room including breakfast for 13 EUR extra. This does not say anything about the price of the breakfast but about the price of a room including such breakfast. Breakfast at fair value is charged with a VAT rate of 19% in Germany. The room is taxed at 7%. To comply with tax rules they discount the room an the price of the breakfast remains at market value (Restaurant Price). You pay the total rate you agreed to for a room with breakfast.