[niels_olson]

> I can't think of a single other example of a single-purpose CA like this.

Department of Defense: http://www.disa.mil/enterprise-services/identity-and-access-...

[rmhrisk]

There are numerous, Microsoft has its own subordinate CA that they operate for their own certificates. Amazon has its own root CA https://www.amazontrust.com/repository/. There are more as well.

[inopinatus]

Amazon is using their CA for issuing customer ELB/Cloudfront certificates, not just their own stuff, and not even all of it: the cert I see at https://amazon.com's is Symantec-issued.