I just read the code in Default.aspx.cs, line 146:
if ((WebUser.IsInRoles("Admins;Content Administrators"))
|| (WebUser.IsInRoles(currentPage.EditRoles)))
{
...
}
As far as I understand, "Content Administrators" can edit this page in any case.
May be, it would be better to change it to
if (WebUser.IsInRoles(currentPage.EditRoles))
only (here and in the other places also), but to make checkboxes near "Admins" and "Content Administrators" checked by default on newly created pages?