They're narrated by Jessica Liu, more details here:
http://ejohn.org/blog/introducing-khan-cs/
Jessica is doing a great job as well... :)
she sounds a lot like Vi, and this comment on this one, 5 seconds from the start helped my confusion...
http://www.khanacademy.org/cs/1-welcome-to-codecanvas/882454...
I'm talking about the actual videos, not the intro one (narrated by Sal Khan and John Resig)
e.g. this one
http://www.khanacademy.org/cs/intro-to-drawing/848372201
Sounds Vi Hart to me...