From a Senate floor statement by Democratic leader (then and now) Harry Reid on May 19, 2005:
The duties of the Senate are set forth in the U.S. Constitution. Nowhere in that document does it say that the Senate has a duty to give Presidential appointees [sic; he means “nominees”] a vote. It says appointments shall be made with the advice and consent of the Senate. That is very different than saying every nominee receives a vote.