Comment 3 for bug 270584

I tried to compile knetworkmanager from svn it complained about missing libnm-glib(-dev) I installed it but configure couldn't find it, because pkg-config won't find it without network-manager-dev.
So, yes you are right with network-manager-dev depends on libnm-glib-dev but otherwise libnm-glib-dev is useless without network-manager-dev and this should be somehow indicted through the dependencies.