[Tallguy]

The chief advantage is that artillery is "on-line" virtually all the time; TACAIR is only available when there are actually aircraft loitering. OTOH, this is all negated if your special forces types are operating beyond the artillery fan.

[Mind-numbed Robot]

My thought is that battles of large numbers arrayed against each other across an organized front is a thing of the past. Terrorism is the method of the next 20-50 years. In this kind of war there is no place for artillary pieces. They are vulnerable to the same kinds of weapons which will replace them. Take Afganistan as an example. Each side had artillary, though not of the sophistication of the Crusader, but American air power and special forces made them of little use. The military of the future will be distant and deadly, complemented by fast and mobile when the battle field must be engaged.