Since gnash can play youtube video, this isn't a restriction in practice. Much ado about very little.
You may be correct that Gnash can currently play youtube videos. But you're missing the point of this article. FTA:
Citizens should be able to download transition-related content in a way that makes it simple to share, excerpt, remix, or redistribute.
The issue is not only being able to view the content using free/open software but more generally being able to do something useful with the video without having to jump through hoops. Especially hoops that have difficult to decipher legal encumbrance.
e-credibility: the non-guaranteeable likelihood that the electronic data you're seeing is genuine rather than somebody's made-up crap. - Karl Lehenbauer