Even the Search Engines are Bad at SEO
Yahoo! allows paid inclusion members to buy quick links in the search results and indexes sites more fully if they use Yahoo! for their site search. While neither of these may seem like a big deal they both are.
Allowing businesses the chance to buy a greater share of the search results or giving them greater indexing priority for them using your search service are both things that would make search purists cringe.
While Google is busy turning the text link into a performance based ad network Yahoo! sells their search credibility and marketshare too cheaply. Buying Del.icio.us and MyBlogLog are not going to make up for the undermining effect on credibility paid inclusion offers.