Please make sure the "Can subscribe" checkbox is checked.
E.g. Usergroup is Registered and they have Standard Access in forum settings. You should navigate to Dashboard > Forums > Settings > Forum Accesses admin page, edit the Standard Access and uncheck the "Can subscribe" checkbox.
I see the same status here on the forum.
I assume that the subscription offer, like my image above, only shows up to admin?
Maybe we don't understand exactly. Is it possible for every registered member to see the offer, as in this picture: http://www.clipular.com/posts/5977600204472320?k=P_z1UpUw2tGzQIZFpsXDGIYbZyo