The AP covered it in 2013, it is not like we didn't know, we just did not pay attention.
That article you are referencing is about a different topic entirely. There is a difference between having public and private accounts, both residing on the organization's servers, and what Clinton did. Kathleen Sabelius's three email accounts were all @hhs.gov accounts. They would have been subjected to the same security and record keeping requirements as anyone in the administration. This is a common practice in private industry, and I expect it to occur in the public sector as well. A well known public figure wouldn't be able to function with every lunatic sending them emails constantly. Therefore you have the public email address forwarded to a team of assistants, and the private email address to conduct day-to-day tasks.
What Clinton did was use a personal email account, like G-mail, to conduct business.