I often smash my volume up key until the volume is max. I usually smash it for too long and the sound is still playing even if the volume isn't actually changing any more. By not playing a sound when the volume is already at maximum we avoid a weird sound and give an accoustic feedback that the maximum has been reached.
Yes, that's what I rely on to know that I'm at maximum volume-when the volume of the feedback doesn't change. If I press a volume key and don't get auditory feedback, that makes me feel like I hit the volume down key by mistake, and I'm at 0% volume.