The answer depends on where you get your numbers from. Fareed Zakaria goes to Canada for his. The reason? Simon Fraser University doesn't count civilian casualties from the war in Iraq. US databases do, and those casualties amount to 80% of the deaths they count. Simon Fraser's numbers (that other 20%) are decreasing and have been for the past several years.
There seem to be numerous reasons for the decrease, but the Simon Fraser study attributes it mainly to the "extraordinary drop in support for Islamist terror organizations in the Muslim world over the past five years." That's like what has been happening in Anbar province in Iraq: the Islamists get too pushy, kill too many of the neighbors, and their popularity goes down.
Counterterrorist operations, including undressing for the TSA at the airport, as on the cover of the May 26 New Yorker (sorry, can't find a good link) seem to be part of the reason for the decrease too. I'm wondering if the decrease in terrorism forms a background for the increasing numbers of people who are getting fed up with airport security theater. Derrick Z. Jackson must have flown lately, and Mike Lukovich's 5/26 cartoon echoes the disdain.