He can absorb ninjutsu without the rinnegan. Look at the last page where his foot was on that shinobi. You can see him absorbing chakara through his foot. I am sorry, but I don't know how to post scans. As you also stated, he absorbed Hashirama's sage mode as well. Furthermore, it would be kind of senseless for Kishi to just make it where Madara simply took off his shirt while saying that amaterasu isn't worth acknowledging. If all he did was take off his shirt, then all Sasuke would need to do is use amaterasu again. This time it would hit Madara's bare body. He could take off his shirt, but he couldn't just take off his entire back or mid-body. Therefore it makes no sense for Madara to have just taken off his shirt. What really happened was this: Amaterasu hit Madara. Madara let it burn for a few seconds while he was denouncing Sasuke's jutsu because he did not feel the need to act immediately. This in turn gave amaterasu the time to burn the shirt off. After gloating for a few seconds, Madara proceeded to absorb the jutsu (but his shirt had already been burned off). That is what happened. PS. If you disagree, I am willing to discuss this civilly. I just say that because some people resort to mindless anger and name calling when people disagree with them, so I wanted you to know that I am not one of those people and I don't want conflict.