From September 2014 to September 2015, Tesla added 858 charging stations all across the US, according to Plugshare. Most of them are not Superchargers, though - Tesla calls them 'destination chargers'.
Tesla's growing charging infrastructure, recognizable mostly for their very powerful, free-to-use (only for Tesla owners, of course) Superchargers, sees a huge increase in installing the so-called 'destination chargers'.
How do they differ from Superchargers? As you already know, Superchargers consist of multiple Model S chargers working together to deliver up to 120 kW of direct current (DC) power directly to the battery. It's a fast way of charging up your batteries to up to 80%, which is usually enough to reach another Supercharger station on your way. In contrast, destination chargers are slower and meant to be used in a situation, when you have enough time on your hands to leave the car parked for a longer while. For example, when you go shopping, dining or when you stay somehwere overnight. It's no wonder then that most of destination chargers have been set up at hotels, restaurants and shopping centers, making charging as simple as it is when you are at home.
If you check the screencap below (curtesy of Tesla), most of the new charging stations are of the destination charging type (marked grey, while the Superchargers are marked red).
We guess, Tesla needs to have all its charging infrastructure in place for when the next models come out (especially the affordable Model 3 EV) in the coming years. If their business plan meets their expectations, there should be hundreds of thousands of Tesla's driving around in the not so distant future, requiring their 'pit stops' to 'freshen up' a little and move on.