When you link your gmail and facebook account with rokurocket, you will notice that the password is asked for by google and facebook and not by rokurocket. You are allowing google and facebook to share information with rokurocket.rokurocket does not have access to your passwords.
This way of authorization is called oauth and you can read more at: http://en.wikipedia.org/wiki/OAuth
In addition to the password being safe, this also give you the option to revoke the authorization at any time. To revoke the authorization, go to https://www.google.com/settings/security
and then Edit Authorizing application and sites. rokuroket is 184.108.40.206