'Picking up' versus 'dressing down'? How about 'listen up, youse guys'? 'Speak up, I say'. The preverb up can be used to intensify the verb. 'Shut up'. But 'draw up' and 'bring up'. 'Lay up' versus 'put down'. Prepositions may start out spatially, but metaphor soon takes over. 'Vote down', 'dust down' versus 'dust up'. Bill's right, sometimes there's very little logic in the ways of language.