Why aerial bombing can't replace artillery

In the same Post story I referenced here, there are a couple of paragraphs about the US Army's concerns with fire support to troops in combat. Fire support includes weapons not carried by infantry or armor, such as mortars, artillery, bombing aircraft.

. . . some in the Army are examining how to fix some of the problems encountered in the offensive against al Qaeda in the Shahikot valley in eastern Afghanistan, in early March. Delays in some airstrikes were a major concern, said two officers involved in that battle. Troops engaged with the enemy always got air support within five minutes, but for other airstrikes -- such as hitting a suspected mortar position so troops could move in its direction -- the average response time was 40 minutes, one of the officers said. Some strikes took as long as four hours, he added.

The delays seemed to come from bottlenecks in the process of getting approval to hit targets. That "target clearance problem" flared into public view in November after Air Force officers complained that Central Command took so long to approve strikes that as many as 10 opportunities to hit al Qaeda and Taliban targets had been lost.

Air support within five minutes sounds quick, but any field artillery battalion that took that long would find itself with a new commander. A couple of minutes is all it should take, and some kinds of missions can be fired in less than that. Artillery fire against enemy mortars or artillery are extremely high priority; to take 40 minutes to attack them is inexcusable.

Thank you, Mr. Rumsfeld, for cancelling the Crusader artillery system. What did you have in mind to do the job instead?