The person responding to the poll has not only been trapped into opining on President Obama's job approval, but their general "feelings" about the candidates. Now the "jury" is locked in by seemingly leading questions that they likely feel they must reflect when they are finally, several questions later, asked how they would vote for president.
So by the time the one question that will be at the top of ballots nationwide is reached, so many other positions and feelings have been expressed in taking the poll that many taking it might not utter the gut response that ultimately becomes a resolute vote.
Interestingly, in this particular survey, people seem to have much higher "positive or somewhat positive" feelings for the Democratic Party than the Republican Party. But later when they are asked which political party they would like to see control Congress, the split is nearly even.
Toward the end of the survey, we see that the percentage of individuals who identify themselves as "Strong Democrat" or "Strong Republican" is relatively low. More say they lean one direction or another or are independent and either lean toward one of the two parties or are just plain independent.
Many surveys being conducted not just nationally but in battleground states are weighted with a larger percentage of Democrat identified responses than Republican. And many, if not most, underrepresent the percent of voters who say they are independent.
In this particular survey, it's hard to tell how party identification is finally weighted. But plenty of other national and swing-state polls make it clear that Democrat responses are weighted higher and the percent of independent voters, who are marching in Romney's direction, are underrepresented.
Polling is an art more than a science, and pollsters do their best. It's just that 2012 is increasingly starting to look like a year in which the polls will have to catch up to reality quickly. There are fewer younger voters and not all voting Democrat this go around; less enthusiasm among the Democratic base; and a giant shift of independents from Obama in 2008 to Romney in 2012.
Anything can happen, but if the vote were held today, it might be a "Dewey Defeats Truman" moment for many pollsters.