Actually this one link does greatly effect your PR as it is a high quality link that google incorporated into their algorithm. If a site cannot afford to pay the fee it is more of a hack than a site willing to invest a mere $299 into their business. If you were google which site would you give the higher PR too; site A which opts for a free directory or site B which pays a fee for one of the top directories on the net. It really does not matter what your opinion is, google values the link.
"There are some directories that DO carry weight - the yahoo directory does a good job..." - quote from Matt Cutts - http://www.searchengineguide.com/manoj-jasra/matt-cutts-on-directorypaid-links.php
if you have money like 60,000 USD from 1 week only then please go ahead and pay to Yahoo. You will be benefited by getting a followed link and they will also remain in business. Good for both parties.
So, that would explain why exactly one of the top ten listings on a particular single plural keyword has a Y listing, and only two of the top ten on the singular keyword have Y listings. I would be more than happy to give you some contextual do-follow links for far less than $300/yr - and they will pass PR as well.
1. There's more value to a good link than just its PR. 2. Only Google measures PR. But it's a strong likelihood that all search engines value a link from an authority site like Yahoo.