That's because each wrapper (which is the gate between the Host and the AudioProcessor) is an AudioProcessorListener, therefore when an object that is an AudioProcessorListener calls setValue() it doesn't exactly want a callback to tell it the value has been set. Think of "setValueNotifyingHost" as actually being "setValueNotifyingListener".
I think to be honest you probablt shouldn't be using theAudioProcessorListener unless you are creating a new wrapper.