I'd like to throw out one more reason besides the lopsided sample that's reason for some cautious optimism. Keep in mind that over the summer, Mitt Romney has basically taken tough punches from the Obama campaign without really fighting back. Soon, he and 527's will begin to spend the money that's been raised, even as Obama's campaign has started spending more than it's taking in, two months in a row.
More than that, for most Americans, Romney is still a blank slate -- aside from the negativity that's emanated from the Obama campaign and its friends in the press. With the convention and the campaign that's really just kicking off (for normal Americans), he's got lots of room to move his "likeability" numbers upward. And unlike the hard-and-fast economic statistics of what afflicts America, there's some flexibility and subjectivity there -- advantageously.
In contrast, the President doesn't have much room to maneuver. The economic facts are what they are. People already know what they think of him . . . and I have long suspected that people who have no intention of voting for him nevertheless protest that they "like" him when pollsters ask, lest ugly racial motives be unjustly attributed to them.
If Romney's people do things right -- and by all indications, they are a capable, hard-working bunch -- the conventions will end with more people knowing things like this, and with a shift in opinions reminiscent of this.