Zbrush normal map projection question

Noth

Hey, I was just wondering how exactly the way ZBrush transfers high res detail to the low poly mesh differs from something like xnormal's hig/low projection. Is Zbrush's more similar to 3DCoat's, direct to texture in the Paint Room? I couldn't find anything about this online, if you know where I can read some more about it that would be appreciated. 

Thanks!