activity-on-node vs. activity-on-edge

the old pert planning book from the 60s that i'm reading uses an activity-on-edge approach, with an appendix contrasting this approach with activity-on-node. at first i was thinking that aoe had conceptual advantages, but i'm not so sure anymore. and it seems that every project management software out there today that has a network representation uses aon. so what is really the difference? with aoe, the edge represents a work process. people say the nodes represent events, but i tend to think of events as things that are externally imposed. i think of nodes on an aoe graph as collectively defining the project _state_; ie, the nodes that do not depend on any unfinished edges at a given point in time define what work has been completed and what can now begin. with aon, the nodes represent a work process and the edges represent products/resources. each task depends on incoming resources and sends its products out through the graph edge pipelines to other tasks. some dummy nodes might be necessary for interface events, just to make the math work, since true deliverables and external resources are dangling edges.