Actually, this is about what it will take for Barack Obama and Joe Biden to win.
Historically, Obama over polls by three to four points, and that was among Democrats in the primaries. This is commonly referred to as the Bradley effect.
Today the Gallup daily tracking poll shows a statistical dead heat between Obama and McCain.
I frankly do not believe that the last paragraphs in the Wikipedia article linked to above are relevant for the general election. The Bradley effect continued to plague Obama until the election was all but decided, and the only person left on the ticket opposing him was when most unpopular politicians in North America, Senator Clinton.
I firmly believe that in order to win, Obama will need to lead in the polls by seven to nine points. Even then, if he wins a sufficiently in key battleground states to squeak out a majority in the electoral College, he will suffer from the same notions promulgated by his Democratic colleagues but only the popular vote counts.