Why do people keep repeating the myth that Obama is the most liberal senator and McCain is a moderate?

I am aware of the national journal rankings that put Obama as most liberal in 2007 (McCain unranked-not enough votes).

link - http://www.nationaljournal.com/voteratings/

But the same ranking has Obama as 10th most liberal in 2006 and 16th in 2005. And the methodology is flawed - they already changed it once after 2004 (after calling the Kerry the most liberal before the 2004 election) and they count something like the Obama(dem)-Coburn(republican) ethics reform bill as "liberal" (the bill bans lobbyists from paying for flights or lunches for senators). So Obama is more "liberal" than Hillary because he did a bipartisan bill with a Republican to diminish lobbyist influence. Hmmmm.

How about this site, done by political scientists and published in a peer reviewed journal?

http://voteview.com/sen110.htm

They find that Obama is 10th most liberal in 2007 and in the middle of the pack in 2005-2006. Meanwhile, McCain is 8th most conservative in 2007, 2nd most in 2005 and 2006. Thoughts?