Not a myth, but varies by airline. I've witnessed bitter discussions by pax with the station manager as they have been un-OPup'ed due to lack of catering for regular meals (meaning someone in Y would have to go hungry or eat their special meal). BA at SFO has this happen daily as they cater to exact count, for example. QF seems to load a few extra Y meals making it less of an issue (presuming op-UP pax accepts eating Y special meal or J regular meal).