Even though Xemnas doesn't have pointy ears, my guess is that it has something to do with the darkness, as they are among the closest to it. Kinda like the Dark Side ruins one's appearance in the SW saga. AkaAxl 15:23, May 8, 2013 (UTC)
Actually, the yellow eyes, pointy ears, and white/silver hair are all traits of Xehanort. Xigbar and Saix (Or Braig and Isa, not sure) are in the true Organization XIII, and Xigbar/Braig admits that he is allowing himself to become Xehanort. Those traits all show that they have accepted Xehanort into their hearts. Xemnas has all that because he already is and always was a Xehanort.