Yorke does have midfield experience but I wouldn't call him a midfielder for the Strike squad...he just wasn't a post up striker. He played similar to how Rivaldo played in the last WC, just off Ronaldo but not quite as deep as Ronaldinho and Juninho (in the early rounds), who had the real playmaking responsibility....Sort of like Del Piero=Yorke, Nedved=Latas, Trezeguet = Philbert. Yorke was a link up man, not a playmaker. His principal job was still to score goals.
Yorke was always predominantly a link up man....he was brought in to ManU to replace Cantona. Even at ManU when he top score he didn't just lean on the last man like a Stern or Van Nistelroy. The reason why Yorke could hold it down in the midfield in ConCaCaf is because the man is an experienced, skilled baller with good technique and a good footballing brain. Even Mark Hughes used to conduct it in the middle in the Premiership (Southhampton) at the end of his career. Ruud Gullit used to sweep for Chelsea, and now goal machine Gudjohnsson is reinvented as a big central midfielder for Chelsea...Intelligent ballers with good technique could move around even when they not that experienced in the position.