So, why not have robots send casually written emails sent at random times using Gmail's SMTP servers?
Yeah, you could - but I still don't think it's authentic :) Actually sending the emails myself also allows me to add small things on the fly - for example, I'll sign my name '-Sandi (fellow Canadian!)' if I've noticed that the person is from Canada.
Though you and others may still enjoy personally sending emails and that's fine.