Given the fact that we can give any number of groups rwx via POSIX ACL's is there any special privileges given to the owning group? For example, we can set any number of users with ACL's but only the owning user (and root) can manipulate permissions. Is it just traditionally how elevated permissions were given to a group of people or does the owning group have additional rights?
Not all filesystems handle ACLs. ACLs are a more general mechanism (gives more finegrained control) than the Unix traditional user/group/others permissions, but are harder to get right. Select what is best for your case.