I know as a TA, it can be hard to answer some questions via e-mail, so I'm assuming it would be difficult to do in a web forum as well. I once spent several e-mails trying to explain something to a student and after failing, asked them to come to my office and explained it in five minutes in a way they understood. So, while there might not be the difference for a lecture, it's the things around the course that can make the experience better.
I know Khan Academy has some problems (at least in the past) with some of its material. One example is discussed in,
http://www.leancrew.com/all-this/2012/12/khan/
I can verify what he's saying is correct as I used to be involved in teaching the same material.
I first learnt C++ in an in-person corporate training session and it was excellent. I think it all depends.