In a recent analysis, Pew finds that news attention to Iraq has sharply declined since last year, overshadowed in coverage by the dominance of the Democratic primary race and the faltering economy. As Pew describes, from January 2007--when Bush announced the "surge"--through the end of May 2007, Iraq had been the dominant story, accounting for 20% of all the news coverage measured by Pew's News Coverage Index. But from the time of that May funding vote through the war's fifth anniversary on March 19, 2008, coverage plunged by about 50 %. In that period, the media paid more than twice as much attention to the presidential campaign than the war.
As a result of the plummet in news attention, the public remains largely uninformed about events in Iraq. A majority of Americans say that they are not familiar enough with General Petraeus to offer an opinion on his job performance, while public awareness of the approximate number of troop casualties in Iraq has steeply dropped from 54% in August 2007 to just 28% in March 2008.
Maybe people feel that the way they can affect the war is through the election (protests sure didn't do anything). So it might not represent a decline in interest in the war per se.