i think it is because electronic music is very technical, and psy especially is very dependent upon sounding a certain way.
you could have a great track written, but without all the technical know-how of mastering, eqing, mixing, the track will not be presented as well as it could be, and not compare to other 'cleaner and fuller' tracks.
in a way it's a shame, because you have such a steep learning curve before you ever make a track that is even 'presentable'. but this would be the same in many other genres such as drum and bass, progressive house, etc.
some of the more experimental styles don't require such a technical labour of mastering, etc, but even then they will still benefit from at least a bit of post-production.