This is an interesting question. They seem to be similar but not equivalent in my experience. The postdoc lasts perhaps 1-3 years while the habilitation may continue on longer (3-7?); and it seems the culmination of the habilitation is a (2nd?) book in the Germanic system and an evaluation by a panel of judges to conclude whether the candidate has passed. This almost seems more akin to a 2nd more advanced PhD or progression to Tenure status in the US system. The culmination of the postdoc instead is completion of a research project and then progression on to another project / job. Thus, similar but not equivalent.