Impossible to disable comments posting to specific node by anonymous via hook_nodeapi

I want to create node where only "admins" can posts, but all visitors may read these comments. I've created node and set option read/write (else admins can't post comments). Then I write such nodeapi handler:

function mymodule_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {
    if ($op == 'load' && $node->nid == 32 /*&& !user_access('administer comments')*/) { // commented for debug
		return array('comment' => COMMENT_NODE_READ_ONLY);
}

Such hook hide link "add comment", but "reply" function is visible. Bug/feature? Is it impossible to make such page by standard comment.module?