This is on my system (number of UID and GID will be different, that is of no importance):
henk@boven:~> id wwwrun
uid=30(wwwrun) gid=8(www) groups=8(www)
henk@boven:~> grep www /etc/passwd
wwwrun:x:30:8:WWW daemon apache:/var/lib/wwwrun:/bin/false
henk@boven:~> grep www /etc/group
www:x:8:wwwrun
wwwrun:x:469:
henk@boven:~>
So, I do have the group wwwrun (do not know why) and it is not used at all, because it is not used as primary group for any user (please believe me, I did check that) and as you see it has no others users attached.
The group www (GID=8) is the primary group of user wwwrun (see the third field there).
Also wwwrun is mentioned as a group attached to group www. Superfluous!