Yahoo! Search Marketing blog notified its advertisers about the changes in bid management "to help you transition to the new Sponsored Search." It explained: What is Changing?
In early December some of the information you’re used to seeing on the Manage Bids page will no longer be available. The “Top 5 Max Bids,” “Position” and “Your Cost” columns will be removed from the current account interface. The View Bids tool will also no longer be available.
Instead, you’ll see two new columns on the Sponsored Search Manage Bids page:
1. Estimated Average Position
This column provides an estimate of the average position in which your ad may be displayed on the results page, based on your max bid and the bids of other advertisers.
2. Bid Range for Top Positions
This column displays the bids for the positions at the top of the search results page for each of your keywords.
Yahoo! FAQs further explain why they have decided to make the changes.