Shop bought chicken

This year we raised some birds for the table and my OH as been the one to butcher them so we have learnt a lot about the anatomy of a chicken.  Yesterday we bought a free range chicken from T***o and I happened to notice that the preen gland was intact but my OH has been removing it from our own birds.  Does anyone know whether this is normal or should it have been removed during processing?  Surely if it is always there it would taint the meat or gravy?  Any ideas?