Well yeah, I mean, OpenGL (to quote Wikipedia) is "a cross-language, cross-platform API for rendering 2D and 3D vector graphics" - nothing more, nothing less. Whereas DirectX (which includes and is often conflated with Direct3D) was specifically designed by Microsoft to attract game developers to their platform (and lock them in) by taking care of all their needs. So it's kind of an apples to oranges comparison...