Indeed. At best all these do is provide a rather basic known-vulnerability check, such as checking for open ports and such. Anybody who is running a serious web site that needs to protect its data should be either hosting with a provider who already provides such a certificate (which may or may not mean anything at all), or should hire somebody to manage their servers in a secure manner. If you're on shared hosting, there are quite likely at least 200 other sites being hosted on the same server. Who can possibly guarantee that one of them is not doing something stupid that allows access to the whole server? Can you really trust all of your hosting provider's employees not to be selling access to the servers? Or doing something stupid like making a quick-access back door for themselves? It's been known to happen.
http://www.darkreading.com/security/perimeter/showArticle.jhtml?articleID=208803634