Unless I'm misunderstanding they did that by partnering with a CA. Becoming a semi-trusted CA themselves. This is not an option for most organizations.
With ACME that will no longer be the case. Let's Encrypt will allow you to do basically the same thing for free with ~20 devices a week[1] starting on February 27[2], for example. In the future, commercial CAs may choose to offer similar services with more relaxed rate limits.
[1]: https://letsencrypt.org/docs/rate-limits/
[2]: https://letsencrypt.org/2017/07/06/wildcard-certificates-com...
[1]: https://docs.google.com/forms/d/e/1FAIpQLSetFLqcyPrnnrom2Kw8...