I feel we all may be reading too deeply into this. What we see of Mayweather on the pads is a very limited presentation of his entire padwork session. All we see is one combination and it's variations.

I feel the reason he uses the pads as he does is merely to practice "punch perfection" getting the arms straight and hitting accurately.

I've tried doing the pads like that for 2 weelks and my punches were a lot straighter and more accurate and I became more aware of where my arms should be.