There is now. 10.8.3 introduced the first OpenGL 4.1 extension (ARB_separate_shader_objects) to Mountain Lion.
Image
10.8.4 might add more extensions. Apple clearly have no issue with adding OpenGL support inbetween the major release cycles. It has probably become a lot easier to perform major overhauls of deeper lying architecture (such as the graphics system) now they don't have to worry about the 32bit architecture anymore. They only need to code, test and debug for 64bit now.