User blog comment:Neowitch/700 - Breakfast at Mugiwara's/@comment-1454981-20130227135301/@comment-4899461-20130227180602

About Shanks and various Devil Fruits. We know Shanks himself doesn't have one, because he had to swim to save Luffy.

Also, Shanks stated that they had recently received the Gomu Gomu no Mi on their latest pirate raid when Luffy ate it back in chapter 1, so he couldn't have been taking it around with him like some kind of treasure from his former captain. (Besides he already had a treasure like that in the form of the Straw Hat, which he gave to Luffy)

And we don't know if Roger had a DF or not, but we can be pretty sure that if he did, it wasn't the Gomu Gomu no Mi. Everyone always reacts to Luffy's power seeing it as "weird" and "strange". Don' you think if the only person to ever be King of the Pirates had the Gomu Gomu powers, people would think it was less strange? And those who knew Roger personally would have reacted differently to seeing Luffy's powers?