backquasI always thought that only Wine and similar software does this work and TF2 uses OpenGL without any conversion layers. Am I right?
WINE converts every single Windows call to a Linux-compatible one, which does often include its own DirectX implementation that remaps to OpenGL. However, that's more of a brute force method. If I recall correctly, Source on non-Windows platforms does map DirectX to OpenGL itself, though because it handles that itself without some wonky compatibility layer, it's going to perform a lot better and have fewer issues.
I believe this is why the Orange Box was on the 360 directly from Valve, while the PS3 version actually had EA as a developer, on top of being the publisher (EA published both). EA was in charge of working on the OpenGL remapping for the PS3, which only runs OpenGL, but the game worked just fine on the 360 which supported DirectX.