I too would like to know the relevance. From a wiki article [1]

In general, Direct3D is designed to virtualize 3D hardware interfaces. Direct3D frees the game programmer from accommodating the graphics hardware. OpenGL, on the other hand, is designed to be a 3D hardware-accelerated rendering system that may be emulated in software. These two APIs are fundamentally designed under two separate modes of thought.

[1] http://en.wikipedia.org/wiki/Comparison_of_OpenGL_and_Direct...