If "self-powered" or "active" speakers are bult in suck a way, that power requirments and speaker performance go hand in hand, why is it that you still get distortion and clipping at the max volume level ?
Because there is a nut loose at the volume control. The amp can only produce so much wattage. You have the ability to ask it to do more. That's when it clips.
Clipping is a function of the amp. If you represent the signal as a sine wave - a series of smooth peaks and troughs - then the amplifier tries to make those peaks and troughs bigger or smaller. Now when the amp is asked to make them bigger, you can get to the stage where the amp simply cannot do this. The smooth peak or trough suddenly goes flat. A peak looks like a plateau (ayers rock for example). A trough could look like a cross section through a boat's hull. This skewed signal is 'clipped' to the maximum value that the amp can cope with.
This happens when the amp is being asked to do too much further up the chain (too much volume or the wrong match of input signal).