And it's open, not closed to one system like ProRes. Personally I have never understood why so many went ProRes when DNxHD is much better when speaking gamma and openness.
Well, one major reason is that to this point there is no DNxHD variant that is RGB (all DNx codecs are YUV, and therefore SMPTE scaled as well). Media Composer can work in RGB, but only by using uncompressed MXF. That's probably one of the main reasons Arri went the ProRes route.