As an investor, Vinod Khosla's job is to make such bold statements. But his statement will never come true.

Even if you assuming that 'doctors' and 'humans' are old technolgy, whenever a disruptive technology has come to market the old technology has not gone away -- it is still used and is often a part of a growing market (this is partly why incumbents are often so slow to move).

Regardless, I think the right way of phrasing the above is that in the future 80% of medical needs will be met by technology. This statement is actually different from implying that 80% of doctors will loose their jobs, it is more that technology will help them do their jobs - either to service more people or to service more complex situations.