Zdravko,
Thanks for posting with this account. Your subscription expired in February, but there aren't any new releases that would change my answer.
When you're logged into Facebook with an administrator of your Facebook app, if you view the Comments box, in the top right, there should be a "Settings" button. Click that, and you'll see a setting for "Other login providers". Check that box. It will allow users that aren't logged into Facebook to login with their Hotmail, AOL, or Yahoo accounts as well to comment.
Unfortunately, there isn't a way to let complete 'guests' or even just Joomla users leave comments. Facebook doesn't have any way to detect users that are on your site, so they can't be used.
Hope that helps, and good luck,
Alex