Oh, the eminent Nintendo designer still answered the question directly. He just said that Peach's flowing gown would have required different programming to incorporate her as a playable character in New Super Mario Bros. Wii. See? Get it? "Skirt issue?"
Destructoid says Wired's Tracey John brought up the question (at the same roundtable at which Miyamoto was told Capt. Lou Albano had died.) Miyamoto's response, according to a transcript: