The Yahoo directory was in the picture long before we worried about page rank. It was there to direct traffic directly to search results. This direct traffic in itself was particularly valuable; and to some extent still is worth paying for in good niches. That's the origin of the Yahoo! review charge. Whether you pay it for SEO purposes today doesn't really matter to Google; somebody at Yahoo is going to say the site isn't utter spam, and that means something... at least a little something.