I'd like to also emphasize how much we lean on our community. Khan Academy's goal is not to be perfect, but to iterate towards perfection — it'd be impossible to do that across such a broad array of content without building up a strong community.
Beneath our videos the community creates Q&A to help address (we hope) misconceptions and follow-ups about each topic (fun example: https://www.khanacademy.org/science/cosmology-and-astronomy/...).
When the original WaPo article was posted, it mentioned a user's question ("So is .02009 greater than .0207?") as evidence of KA failure. But to me, the fact that there were already helpful, patient responses to this question from our community...well, that's a success. We know KA can't magically teach everybody everything, and building a community of support is one of our biggest goals.
Of course, we also use the gems in this community to help us iterate on content.
Sal goes back and reworks videos often, but this is difficult to scale so we recently added the ability for us to make "official clarifications" from our community's content. These are video annotations that clarify important or confusing points for videos we haven't had time to redo yet (see an example at 12:47 in https://www.khanacademy.org/science/chemistry/acids-and-base...).
Overall, Sal has imbued the entire company, starting at the top, with a belief that shipping beats perfection.* We're building tools to move as fast as possible any time we can improve our content — but that won't stop the occasional valid criticism from surfacing. We'll make use of it.
On a transparent/personal note, I take issue w/ many of the assumptions and tone behind this letter...but my shortcomings here won't stop our team from plucking some value out of it.
* https://sites.google.com/a/khanacademy.org/forge/for-develop...