Why? Khan Academy is a non profit organization. They are not looking to make money. They are trying to change the world of education.
I am impressed by these numbers because it means that more people are now aware that there is a quality free resource where they can educate themselves.
Yes, money is a validation if your goal is to make money. If I am a for-profit company and I show you millions of visitors for my website but no real revenues, I would agree that it's not impressive.
As the other commentator pointed out, their goal is not to make money. And this is impressive because it's a huge progress towards their stated goal.
"We're a not-for-profit with the goal of changing education for the better by providing a free world-class education to anyone anywhere." http://www.khanacademy.org/about
I am impressed by these numbers because it means that more people are now aware that there is a quality free resource where they can educate themselves.