The way it is control in Plone is via the document_byline template macro, invoked in the bottom of the document_view template and other. There are two options to get the date and contributor removed:

1. Simply remove the reference to document_byline in your template views and you're done.
2. Modified the ploneCustom.css in your portal_skins/plone_styles add the following line:

        .documentByLine { display:none; }

In my opinion this is follows the design of Plone2 which attempts to control everything from CSS.