If Johnson is taking votes from those who would otherwise be voting for Obama, then that’s not a de facto vote for Obama. But for Freepers who would otherwise be voting for Romney, picking Johnson is more or less a vote for Obama.
On the Logic Scale, that rates a Duh (no offense intended).
Per your reasoning, that would count as a vote for Romney.
That's the part of this reasoning that fails, in my mind. It's the assumption that a person's vote is somehow owed to the party with which they most closely associate.
Political parties are an invention that have nothing whatsoever to do with our system of government or the root tenets of our founding. If one believes in the Declaration of Independence, the US Constitution, and the Bill of Rights, then they most likely see themselves as a free citizen, unbeholden to any political party.
In that wise, their vote is their own, and is sacred. The very thought that it's somehow owed to one party or the other cuts against the very grain of what it means to be an American.