ARB stands for architecture review board. The functions and constants ending in ARB are extensions to the opengl core profile. These don't have to be supported by the hardware but it gives the hardware designers to show off how clever they are and how good their product is. (The architecture review board is a board of the companies that make the hardware, Nvidia, AMD, Intel, Apple etc.)
As far as I can see, most ARB extensions (if not all) become part of the core profile when the next version of opengl is released. So the ARBShaderObjects extension was probably added in opengl 1.3 or something around that then when 2.0 is released, low and behold, shaders are a standard feature. In conclusion, the methods are exactly the same in every aspect but name.
Edit: Said the wrong thing.