True. And there's always the possibility that usage of a particular station might improve if the station was served more frequently. A good example is Newton St Cyres station which serves a village with a population of 867, according to Wikipedia. 1,784 passengers used the station between 2010 and 2011 - a figure which would improve if every train stopped there on request (the only trains to Exeter St Davids booked to call by request Monday to Friday are at 0758, 1815, 2009, 2119 and 2308; trains to Barnstaple call there at 1804, 1904 and 2107.
Not sure Newton St Cyres is a good example. The station is half a mile down the lane from the village, which is on a main road with lots of buses to Exeter, journey time 14 minutes. Mind you, the station is adjacent to a very good pub: http://www.thebeerengine.co.uk/index.html