I wonder was it a bit of artistic license
I wondered about that too. If the pad were in place on that arm it would reduce the dynamic some, but then he would just increase the perspective on the arm, make the hand bigger to maintain the dynamic...so I think Cam Kennedy probably forgot to ink it in. No criticism, Dredd is a complex character to draw and I'm surprised more artists don't forget bits and pieces.
It also says something about the quality of the artist's storytelling that nobody noticed

Frankly, I think that makes it EVEN more valuable.