Managers, salesmen, accountants, designers are not being replaced, but their jobs are being enhanced and made more effective by technology. And consider the Da Vinci Surgical robot that allows a surgeon in Baltimore operate on a kid in South Africa.
There are plenty of jobs available for kids that go to technical schools and learn basic trades (many of which are now high-tech) and the oil fields in Texas and North Dakota are screaming for workers.
Much unemployment today is due to kids going to college and majoring in something that doesn't prepare them for a job.
All this said, yes, sometimes people get replaced and/or just fired. New technologies come along...some companies simply fail.
So those people will have to retrain and sometimes move...but such is life.
Certainly in some countries but not here.
Big Education is integral to the progressive control of society.
Actually, the Kahn model by itself could not replace classroom teaching entirely - Kahn himself said that was never the original goal of it. At the moment, it is designed to enhance and complement classroom learning. In order for an automated technology to make classroom teaching completely irrelevant, it would also have to replace teacher student interactions and individual tutoring and be able to help with individual questions the way a teacher would. As much as we rip on public school teachers - and yes, of course, tons of them deserve all the abuse they get around here, the Kahn Academy and the MIT open courseware by itself cannot make classroom teaching irrelevant.
A technology that can actually make classroom teaching completely irrelevant would also make scores of other vital jobs irrelevant as well and continue to place millions out of work, at least temporarily while they are forced to adjust and learn new trades. And in our nation, this would damage the economy since, regardless off what we prefer, we are not at all prepared as a country to have these Americans go without food or shelter of any kind while they learn these new trades and make themselves employable again.
So as far as teaching goes, if automated systems can make classroom teachers completely irrelevant, then in fact they could do the exact same for managers, salesman, accountants and designers. When you can fundamentally replace one type of human interaction like that, you can see that it is only a series of small steps before tons of other types of human interaction get replaced entirely as well.