or did he give it up for another reason? I can't remember…
This page should answer that.
As for Shanks. On this page and this page Whitebeard is talking about how the 'old days' were legendary and that time passed so fast, and even Shanks' duel with Mihawk is new to his ears. (the way he brings it up makes me believe that this was part of the older news from that legendary time ~~ since why bring it up like that unless it were old news?) And then he says everyone was so surprised when you came back without the arm ~~ then asking what kind of enemy he gave it to (suggesting they were a formidable opponent if even Mihawk could not take it). Just what I see in all of this though…....