Well I can't help you with pictures but I can tell you the difference you asked about; by just running 3" pipe from the turbo elbow down you still have a fairly large restriction at the elbow itself. A full DDP will not only eliminate this resriction by utilizing a much larger elbow, it seperates the wastegate exhaust outlet to a seperate exhaust tube running alongside the bottom of the downpipe. Under boost when your wastegate opens up, instead of the newly introduced exhaust "tumbling" into the existing exhaust stream, it is dumped seperately without disturbing existing exhaust flow. Remember, on a turbo car the less exhaust restriction the better (to a point -- you don't want to run 4" pipe unless you're pushing 500+ rwhp for example; 3" is good to 400-450).
Hope that answers your question.
