We have seen their feet when they were the stealth, disguised Others. Now that their gig is up, they wear shoes.
OK, but I don't think we have specifically seen Richard's feet. Maybe he is the last of the original island inhabitants.
True...I still can't get Sawyer's line from "Live Together, Die Alone" out of my mind about how he thinks the Others wear beards, because they are all aliens. lol Clue or in-show parody?