Anatoly does a great job of explaining the event types and why you really only need 5 or 6 of them to fully express process models in BPMN.? Personally, this chart of event types to situation perfectly illustrates the absurdity of 19 event types, out of 30 possible.
And that is after Anatoly pruned from 8 down to 5 event positions!
The unfortunate issue with BPMN 2 is that much was added that isn't necessary. Lots of emphasis on completeness and not enough on brevity or "editing" down to what is necessary.
The practical set of needs is a significant subset of everything possible.? This is one of the challenges of a notation - without an implementation to make the notation concrete, philosophical or theoretical differences can loom larger than they really are in a practical implementation of the same ideas.