I think they didn't use a ramp or catapult to launch the Me 163 because A.Lippisch used for this project an idea of a glider without a tail.Besides the rocket engine power of Comet was under pilot's control after it had been started so it was possible to take off from an airfield using classic undercarriage.According to this consumption of the fuel didn't matter.The V-1 rocket missile was powered with a pulse engine which needed an air to work properly.Having no axial compressors of its engine the V-1 had to be launched with a catapult in order to get the air movment in the engine.But it is my opinion only.