It's not hard to believe that McCain was ahead in Missouri on August 7th, 2008, by a 50-44% margin at all. First of all, he actually won the state. Second, the RCP average of polls on Aug. 7, 2008, the day of the poll you linked to, had Obama ahead nationally just 3.6 points
http://www.realclearpolitics.com/epolls/2008/president/us/general_election_mccain_vs_obama-225.html, a far cry from Obama's actual winning margin of 7.3 points.
So yes, I get you're trying to say that Rasmussen shilling for Romney with this Missouri poll. But if you look at where McCain stood on that day in 2008 polling-wise, it isn't shilling at all.
