It is why incongruity should give us pleasure, and why some sorts of incongruity prompt laughter and others (such as Oedipus' parenthood) do not.
Perhaps, but consider Oedipus Rex by Tom Lehrer:
There once lived a man named Oedipus Rex,
You may have heard about his odd complex.
His name appears in Freud's index
'Cause he loved his mother.
His rivals used to say quite a bit
That as a monarch he was most unfit
But still in all they had to admit
That he loved his mother.
Perhaps, but consider Oedipus Rex by Tom Lehrer:
I don't care who you are, that's funny.