I'm wondering why some OpenGL examples I found were always checking that some extensions were supported by the graphic card before making the corresponding OpenGL calls. As instance, making sure the graphic card supports "GL_ARB_shading_language_100", and then using the core function "glGenShader(..)". I thought these extensions were to be checked for "...ARB" functions only, since if the graphic card supports a version of OpenGL, it also supports all of its core functions... Or am I wrong ?
I'm also a bit confused with other extensions which have no associated GL calls, such as "GL_ARB_texture_non_power_of_two". Is it also concerning only ARB functions, or does it count for all "texture.." functions ?