Hacksaw,
The strategies are fundamentally different. In classic insurgency, you build up a structure in an environment controlled by an existing political structure; AQ's new model is to undermine an existing structure with a barely coordinated/semi-viral organization until it collapses, then move in. At first glance the AQ seems nihilistic, but the apparent nihilism is step 1... At this level, one major difference is that most historic insurgencies had a political campaign but that is optional for Islamic based insurgency, as they do not distinguish between matters of religion and matters of politics.

Islamic aspirations to Caliphate are their 'supreme ultimate' under divine guidance, where communist ideologues were at best useful-idiot true believers. Given that the communist followers were under the impression that they were fighting for workers, equality, etc, there was common ground to undercut the ideology through negotiation. AQ does not allow that; convert and accept the caliphate, or die.