The relative merits of the 2 APIs have diminished over the years. For high end realtime rendering they merely act as shims for managing various kinds of buffers

The relative merits of the 2 APIs have diminished over the years. For high end realtime rendering they merely act as shims for managing various kinds of buffers and activating the shader code for processing those buffers. The rasterisation stage at the end is tiny nowadays. You need separate render paths for different hardware on both D3D and OpenGL. Neither API gives you a fundamental advantage, it's really just a matter of taste and destination OS. I expect the API call layer of their engine to be tiny and interchangeable, think Direct3D 9 vs. 10. (their engine already supports some consoles, too)