StartSSL is able to do it because they cut out the nickle and dimeing BS. They state it clearly on their page, it costs them practically nothing to issue their

StartSSL is able to do it because they cut out the nickle and dimeing BS. They state it clearly on their page, it costs them practically nothing to issue their class 1 certificates because the process is automated, so they simply don't charge for it. I would guess it's easy for them to do it since it's their business anyway. As for the others, it's probably too much of a hassle to set up and maintain a public CA.