Ordinarily Yahoo embeds a "shortcut" link to one of their properties for certain queries. For example, if you do a health related query there will be a link to Yahoo Health. In this instance, it seems this is the first time Yahoo is pushing users from the search box to another section of their website. The difference between a regular query and a webmaster query is that the webmaster serps all come from Yahoo. Still, it's notable that this is the first time a search takes you to a different part of Yahoo.
It only goes to page 20 and if you have a sitewide link, those links saturate the listings leaving out a lot of other links. Not Good at all. Yahoo should condense sitewide links with "more from site" otherwise its only MSN now to check all you links.