This article is not based on their "snap poll". It is based on their daily tracking poll which they have been running now for a week or two with The Washington Post. The margin of error on this poll is 3%, so a 4 point difference as is the case here is just barely beyond saying its a tie. Bush lost three or four points following the first debate. It could happen again based on events in the world or an error by the President so better to not get overconfident based on polls. Read Michael Barone's article today on RealPolitics.com for discussion of polls and turnout.
Sure that's the right URL? I get redirected to a list of links to stuff like DU and smirking chimp.