Indirectly, yes. The sub by itself does not relieve the burden of reproducing the last one to two octaves. The passive attenuation circuit does that by filtering these low frequencies so that they never reach the main speakers. That way, the mains can concentrate on the easier-to-reproduce signals above 80Hz or so.
Sub Question
I tried to do a search, but could not drill down on this. Anyway, I have never owned a sub. I never really felt the need. However, I had a friend tell me that a sub does more than just enhance bass output and perhaps bass quality. He went on to say that having a sub takes pressure off the driver thus making the speaker do less work. Because of this, the speakers will sound better or have better clarity. Thoughts?