I would think that the human input is improving the OCR algorithms. I assume that every human correction trains the OCR in some way. With enough corrections the OCR should at some point learn to distinguish between the characters it couldn't before.
Which means the technology will eventually make an algorithm so good that it can solve a CAPTCHA as well as a human, thus making itself obsolete. What other technology does that?
Only the ones that are too aggressive. Most viruses shoot for a very nice balance between killing the host and keeping enough of them around for the next batch.
The weirdest effect of this is that the most dangerous viruses tend to burn out. If one of those ever came along with a really long incubation time for the disease but a much longer time for contagion that might be a problem.