Their offense helps their defense tremendously; just like ours does. Their offense is a heavier run offense which keeps the clock rolling. If you watch the clock as they snap the ball, they go very deep into it, this cuts down on the amount of possessions for them and the other team. Therefore, there are less possessions, there is also less time on the field for the defense so they are more rested. Their offense also has no problem trying to pick up a first down or two and then punting and trying to pin the other team deep into their territory, this forces the other team to be a little more conservative and burn clock.
One thing that has changed for Iowa this year will be their punter, last year people started figuring out that you need to send a couple people at him and force him to kick quicker, this doesn't allow the gunners to get downfield as quickly and allows either fair catches or something of a return. He also shanked a couple against us this last weekend, so it does make a difference.