Google used to have a feature that allowed you to watch videos from YouTube and Google Video inside the search results. Launched in May 2007, the video plus box was a quick way to play videos without having to load the entire page of a video hosting site. For some reason, Google only limited the plus box to its own video sites (YouTube and Google Video), while showing thumbnails and metadata for other sites.
Yahoo Search added a similar feature in October for YouTube, Metacafe and Yahoo Video, but now the plus box is nowhere to be found in Google's results:
Instead of making the feature available for other video sites, Google decided to remove it altogether. Hopefully there's a better explanation than increasing the number of page views for YouTube and Google Video, as Google usually puts the user first.