In a 2008 redesign, Facebook introduced an improved status-update toolbar, called the Publisher. In addition to just writing and publishing a status update to your news feed and Wall, you could also add attachments — links, photos, videos, events, or content from third-party applications.
But third-party apps were defaulted to a dropdown tab. And not many people used it, Facebook says, so it is planning to remove the attachment dropdown entirely; its own applications will presumably stay on the tool.
Given the dropdown’s apparent lack of popularity with many users and developers, the impact of the change should be just as minimal.
Update: A vocal group of developers say that they have been getting good use out of the Publisher dropdown, read more on this forum thread.