Anatoly's 2nd BPMN Assumption is that the organization has mechanisms for task assignment and transfer.? This is, strangely, one of the things that trips up people new to BPM.? Why?? Because in traditional flowcharts, the hand-off is something you would likely model or draw.
And, because often they don't know how the BPMS works, so they don't know that these hand-offs are handled transparently by the platform itself, typically requiring no code at all.
But the final reason is that it is simply the right abstraction and simplification of the model to not explicitly model these deadweight items.? In the diagram below, crossing swimlanes and starting a new activity implicitly transfers control to a new group (Accounting), and initiates a new task for a member of that group.
It is also surprising to me how much code goes into handling these assignments and transfers in traditional software platforms that are not BPM or Workflow friendly.