Comment by servo_sausage

I've never heard it in terms of courtesy, more that a human employee is an entirely different category to some mechanical component of a business.

So the setup goes, if a doormans function is defined as opening the door, then he can be replaced by a cheap mechanical thing; this misses that he is both covering more incidental tasks, and providing a human interface to the business. These things are very valuable, but not captured in the "guy who operates the door" definition.