Perhaps, didn't read that. But this tape is such an outlier from previous behavior that it even took the Jihadi's on the internet off guard. From Fullwave @ TT, they still appear to be trying to figure it out too.
If we accept that this is psy-ops (whether or not it is actually followed by an attack), then it may be helpful to view this in the context of the dilemma faced by authorities each time they must consider how to respond to a given threat (for instance, how to deal with the alert level).
The enemy psy-ops have value to them even if no attack follows a threat as it generates threat fatigue leading up to actual attack, incurs economic cost if an alert is issued, and probes our defenses by attempting to force us to "show our hand".
The value of enemy psy-ops increases exponentially as the potential domestic audience increases. The immediate pre-election environment is ideal for them for this reason as the potential political impact of threats and associated potential attacks have enormous relevance to an extremely tight election where national leadership could be decided by several thousand if not several hundred votes in a handful of key states in a nation of close to 300 million.
For an enemy psy-op communication to be effective it has to be communicated. Jazeera has taken to editing and even withholding tapes. Internet sites can be shut down and authenticity is more questionable, so it was physically delivered in Wazirstan with Sahab "markers" to signal it is a bona fide AQ tape.
Why ABC? Foreign broadcasters can more easily suppress the information. Delivering this directly to an American outlet is not a hot potato, it is a hand grenade. It is much more likely to leak (even if it is never released) in an American rather than a foreign context. And even if the entire tape is never released, much of the sought damage is already done by virtue of its simple existence.
Put yourselves in the shoes of an adversary and ask yourself how it might be possible to (at least temporarily) politically destabilize the United States.
It cannot be done easily, but possibly at very specific times under a certain set of conditions a very short window of opportunity could be created. Actions will be sought (psychological or physical) that maximize uncertainty. Counteractions should be sought that maximize certainty, confidence, and legitimacy.