The 'can have PR but not pass it on' penalty: Possible high PR. Google do count links to the page (PageA), so PageA gets high PageRank and ranks well for its words. But, because of the 'can have PR but not pass it on' penalty, the person who buys PageRank (PageB), doesn't get any PR from PageA. Other pages on the same domain as PageA do get PR from it, and if PageB has enough PR to show backlinks, then PageA does show the link, even though it doesn't count.
wouldn't it be fair to ban the "PR-Seller" by taking away his PR, instead of giving him the chance of making decent cash off newbies with deep pockets?