I'm not sure exactly what version you are using, but I think your network manager is just not running properly.
I am on Ubuntu 10.10 with network-manager package version 0.8.1+git.20100810t184654.ab580f4-0ubuntu2 and that bus exists for me.
Also, the official specification states that in 0.8, that bus exists:
http://projects.gnome.org/NetworkManager/developers/spec-08.html
I'm not sure exactly what version you are using, but I think your network manager is just not running properly.
I am on Ubuntu 10.10 with network-manager package version 0.8.1+git. 20100810t184654 .ab580f4- 0ubuntu2 and that bus exists for me.
Also, the official specification states that in 0.8, that bus exists:
http:// projects. gnome.org/ NetworkManager/ developers/ spec-08. html