When words and truth no longer matter

In this clip from the Daily Show Jon Stewart shows the discrepancy between what President Bush told listeners in a radio address and what two army commanders had reported in Congressional testimony just two days previous. Donald Rumsfield is also in the clip giving an "answer" that is a classic example of Orwell's "pure wind" political language. Why is it that a comedy news spoof is doing the work that actual news shows should be doing?