SDTV ad fit for HDTV - relation to RSS advertising
One of the challenges of running the world's largest RSS advertising network is that most creative agencies don't have off-the-shelf creative optimized for an rss advertising campaign. your choices are usually to wait for optimized creative or use another creative size that has already been created.
HDTV advertising faces a similar challenge. You can see here in this picture that as of today, ESPN just runs SDTV ads and puts "HD" sideboxes on the side to make it fit the screen appropriately.
Both these things will change over time. As more and more agency teams get used to developing creative for these new formats, the more optimized creative you will see, as there will simply be less friction to getting a campaign running on time.