We cannot just assume that everything that is automated is something we need to stop simply because it is automated.
Maybe the design of email is the problem?
Maybe the design of blog comment systems are the problem?
CAPTCHA's are aimed at stopping automation. That appears to be the only criteria they filter on. It just seems strange.
Of course CAPTCHA's will eventually be useless. Because most of us are working our tails off trying to push automation forward, not find ways to block it simply because it is automation.