This policy seems to be a relic of the times before google docs allowed 10gb files of any type. Because the two services share a purchased storage pool but have different policies regarding taking items out.
My assumption is this will disappear, especially with how close google is tying Picasa to google+, i.e photos and videos uploaded on google+ are stored in Picasa. Not being able to download videos from google+ kind of defeats the whole data portability argument google keeps talking up and using against facebook.
