The Chicago API has features that do not exist in any other implementation in the world. This is because:
A) The vendor in this case (ConnectedBits) added features to the API that have been talked about on the Open311 mailing list just because they can.
B) The environment in Chicago is complex enough to require features to be added to the API in order to accurately reflect the workflow and "relatedness" of service requests.
The API documentation will hopefully make it easier for Chicago developers to make sense of the Open311 API in chicago and get involved. Also, the site is being built in a generic way so other cities could use it to describe their Open311 implemntations, too. If so desired.