POST services hooks do not include tags or refs information.
When using the POST service and pushing a tag to a git repo (untested with hg) there is no information about the tag being pushed in the payload sent to the endpoint.
Additionally there is no refs information such as
(see here for example)
I am not suggesting that the services match githubs exactly (that would be nice though), but perhaps some inspiration could be drawn from them. As currently the information in a payload is either lacking, or superfluous (every commit in one array).