"the budget cuts he seemed so giddy about invariably mean fewer teachers, and to argue that this is somehow beneficial to learning is to argue against years of research and practice" -- this is exactly the argument that Khan Academy is making: that we can cut teachers in favor of lessons taught by computer. The actual reason why "this time is different" is that we now have the power to create excellent lessons, through the power of computers, the internet, and crowds.
Maybe Khan Academy isn't good enough to replace teachers yet. (I would be surprised if it weren't already better than 75% of teachers, though. Most teachers aren't very good.)
Another claim the author makes: "Khan Academy makes it difficult for something better to come along" -- I would be SHOCKED if this were true. Sure, it's hard to compete with free, but KA is creating a new ecosystem of people who are looking to the internet for teaching materials! So if KA is really as bad as the author claims, then it's going to be MUCH easier than it is today to get better materials in the hands of kids.