Using an if exists statement with author info tags

I’m trying to use an if exists statement to determine whether or not a commenter has entered a link, and apply different classes/include different info depending if they have or haven’t.

Figured something like this:

<?php if (function_exists('comment_author_url_link')) {
	echo 'yes';
	} else {
	echo 'no';
} ?>

…would do the trick, but it displays ‘yes’ no matter whether or not the commenter included a link with their comment.

I had asked a similar question a month or so ago about using an if exists statement with custom fields (link), and scribblerguy was kind enough to help with an undocumented function.

Is there a similar undocumented method of doing this? Or am I missing something really simple? ??