The article's main criticism is that KA doesn't try to talk about all the possible uses of the subject matter. I'd rather they didn't, or at the very least kept it separate. Unless someone's being forced to sit down and watch educational videos, that doesn't add enough value to justify the time spent.
It may be that other competitors (including the ones you've mentioned) will try to fill the gap and take a more traditional education role. But saying something's bad just because it's not occupying the exact niche that the author wants it to? That's not a very useful criticism.
I'm no teacher but if I was I'd much rather spend my time getting kids excited about stuff and then point them to the resources they need to get going. I'd also have more time to answer questions so the kids wouldn't get as frustrated or stuck.
I'm sure Henry Ford had people who thought cars were a bad idea.
Carry on.
"Khan Academy and its donors may preclude better products from coming along"
I just don't understand this. KA, Udacity, Coursera, Codecademy, MITx, teachontablo.com, this list goes on. I don't see how KA has done anything but prove the possibility of traction. When professors like Thrun and Norvig and investors like Paul Graham, Fred Wilson, and Peter Thiel are excited about the educational space, I believe the students will eventually win. It's no secret that many of the above have been inspired by Sal in one way or another.
The more products competing here, the better education will be. Yelling at Khan Academy because it's "the only thing that [exists]" feels...oddly misplaced.