Oh, I agree, a massive terrorist attack could be likened to a Kobe earthquake - massive casualties, no warning, etc., but localized. In addition to that, though, we have the psychological impact on the rest of the nation.
That is what would be (partially) fought by information. The temporary loss of the Internet would create a black hole, within which all sorts of misinformation and rumors would sap Americans' gumption. Long-term, though, a major terrorist attack would have psychological implications so severe (loss of feeling secure, long-term plans being abandoned, etc.) that whether the Internet were up or down would not matter.