Here's why. (Reader Omegatron pointed us to the FAIL blog that captured this beauty.)
Notice the messed-up horizontal scale, in particular, the failure to start the axis at 0. The result: the tiniest difference presented as a wide gulf.
The graph, published by the Washington Post, has since been fixed. See here. Nevertheless, the comments left by readers lent witness to the confusion. I copied the first bunch that mentioned the graphical display - there were plenty of for-and-against-the-prize comments, many assuming that the poll result was as lop-sided as the chart seemed to indicate.
Posted by: Tomcat3 | October 9, 2009 8:53 AM
Posted by: jonbwnfd | October 9, 2009 9:40 AM
Posted by: subwayguy | October 9, 2009 9:48 AM
Posted by: T-Tom | October 9, 2009 9:53 AM
Posted by: cmcintyr | October 9, 2009 10:02 AM
Inconsequential detail? Big fail? You decide.