They don't lie.
or
So that real estate agents would have someone to look down on.
or
Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
Three skunks fighting over a pickle
First dog: My master calls me Furball. How about you?
Second Dog: My master calls me Sitboy
or
Finding a cabinet position for the thing on his head!
or
Only one, but they get three tech. reports out of it.
or
Because they are black and white.
or