It might be next to impossible to stop, but they did stop 2 women suicide bombers during the voting. How many others were scared off because of the extra security and no cars to use to run away?
However, I agree that the bombings are done to change American minds, not Iraqis. The terrorists are EXTREMELY media savvy...something they learned from their Viet Cong comrades. Just look at how they reacted in the note from Zawahiri about muslims killing muslims...it wasn't going over well in the media.
It's a good thing the Axis powers didn't get this type of coverage by our media sixty years ago.