"Wet location" mains outlets
Reading your question and the other comments, I'm just answering to try and sum things up.

First a Weather Resistant Receptacle. Provides compliance with 2011 NEC Article 406.9 that states that all receptacles installed in wet and damp locations must be weather resistant.  “WR” designations provide visual identification. Weather Resistant Receptacles offer protection from rain, snow, ice, moisture, and humidity when properly installed in an approved weather protective or while-in-use cover. Weather resistant receptacles are for use in any residential or commercial outdoor location. Designed with enhanced nylon and corrosion resistant metal components Weather resistant receptacles are extra durable. 

I think the electrician was just trying to give you the best job he knew how, even though it isn't necessary. Either that or that's the only receptacle he had on hand. There is no problem with installing better than code minimum.

Hope this helps.