Triple buffering is an updated feature/version of Vsync. The double buffering is what could lower frame rates to 37.5 FPS if the GPU dipped below 60 FPS. I believe, correct me if I'm wrong, that triple buffering makes it so it doesn't have to lock at the 37.5 and can keep a higher, constant frame rate in while maintaining the sync.
From my understanding, the double buffer of Vsync will lock at different intervals of FPS. 60 being the norm and the highest, but as soon as the GPU outputs less than 60 FPS, it immediately locks down to 37.5 FPS in order to keep the sync because of the way the buffering works.
There are some nice articles on the net that probably explain it better than I can. >_<