Because you can make anything about process: the back and forth between the campaigns was also remarkable for the sheer speed with which it happened. It was like following a conversation — a not very friendly one — in real time. It’s obvious that the Obama camp would want to hammer McCain on Iraq, what’s less clear is why McCain would eager keep the story alive. I suspect both camps would just rather talk about anything than the economy, which has metrics of a more immediate kind for most Americans.
Not that talking about Iraq isn’t important, and immediate, to thousands of people (especially Iraqis), but the two candidates have both made their positions on Iraq their brands, and neither of them inspire much trust when it comes to the economy — Rasumussen even has McCain beating Obama (but within MoE) by a hair.