so you mean that every game made is made with opengl or direct3d ?
No. He said that games could be using
C: Your own drivers and custom API
D: The drawing API provided by the OSes of choice.
Naturally you can also create 3D games using C and D. Take a look at Quake, for instance.
That's software rasterized polygons. Simple 2D raycasting can be used to create games like Wolfenstein 3D (and Doom, if you're clever)
You can access much in cross-platform drawing through the use of browsers. It's easily the most cross-platform way to create games, and doesn't necessarily depend on OpenGL (That's the browser that decides on rendering.)
So there's no rules as of what to use where.
Only it's probably more common to use existing API's for Hardware acceleration when developing 3D applications (As Olof said, most modern 3D games use them)
Naturally, higher level frameworks and libraries such as SDL allow even more abstraction than basic DirectX and OpenGL.