On _Cheers_, there were several references, one by Frasier's mother [[anyone
  care to confirm that? I've never seen that episode]], that Frasier's father
  was a scientist who had died.  But in _Frasier_, he is a retired police
  officer.

  In the "The Show Where Sam Shows Up" episode, Frasier says that he told the
  gang at Cheers that his father was dead because he and Martin had just had a
  fight.  When Martin asks Frasier why he told them he was a scientist,
  Frasier responds, "What did it matter?  You were dead!"

  Apparently, the creators decided that _Frasier_ would be a better show with
  Frasier's dad than without him.