Why does a two prong recepticle have a ground screw?

[ptonsparky]

The same reason men have nipples.

It makes more sense to have one basic design and tweak it with a few simple changes to create different models.

I like 220s anwer best.

If we have to put a ground screw on a switch why not a 2 wire recept?

 

[iwire]

If we have to put a ground screw on a switch why not a 2 wire recept?

I was under the impression two wire receptacles are generally used where no grounding means exists.

If there is a grounding means available wouldn't we be installing a three wire receptacle?