Given some of the criticism of your YouTube videos, I agree with your simple advice: Let them make something better and let the viewers decide.
The Khan Academy does not have some kind of monopoly on providing education content to help people of any age learn. Rather, the Khan Academy was simply the first to resonate with so many people around the world in such a short period of time. You clearly have many people's attention.
The Internet is an open medium to provide content, and to those who think they can do better, they know that they don't need much to get something up, as has been made very clear with Sal and his use of a simple drawing tablet, screen recorder, and headset. So make it happen -- show how your content is vastly superior to Sal's that both educates and makes it fun. Oh yeah, and free.
Sal, as you have noted a few times now, you are actively looking for other people that posses your talents to educate people. Have you thought about creating an open competition on your site and let the public vote on what they think is good content and fits the "Khan Academy mold"? Just a thought :-).