A lie.
Technically, you are correct. If you do not vote that cannot be counted as a vote...for anyone.
Realistically, if you are in a swing state and do not vote where you would normally have voted for McCain...you improve Obama’s chances of winning.
If you are in a state that is pretty much locked up, as I am, it will not make a difference.
Once caveat...Remember Florida!
No, actually true. Anyone who doesn't believe a vote for Barr or similar 3rd party candidate isn't a vote for Obama doesn't remember recent history well. In '92 to the Perot vote took away plenty from G.H.W. Bush to get Clinton elected with just 43% of the vote, in '00 the Nader vote siphoned enough from Gore to elect G.W. Bush.