Incase no one bothered to tell you, StackOverflow, SuperUser and Serverfault are the original implementations of this style of user interface. Doctype came afterwards, and since it is related to what we do, we linked to them.
Those 3 sites actually run on the same software StackExchange runs on, which makes sense because StackExchange was the product of StackOverflow's success. They took the user interface and made it available to others for a charge.
However, we are the originals. And the source-code is not open source and/or buy-able (for under a couple million)
I'd like to put this under the [generation-gap] tag. It seems like everyone just assumes that a site is built on another site's framework or an open source project. While StackOverflow does have some OpenSource components, it was pretty much developed ground up.