I take on board all your comments and you are both right on various points, however I was trying to give a general view of how diesels work and stay away from vehicle specific details such as the shut down flap on the VW PD family of engines and so on.
You could say that they have a positive pressure in the manifold because of the turbo, but that opens up a whole new tin of worms.
EGR like so many other systems have been with us for many years in lots of formats (internal EGR generated by valve overlap as an example) and is still missunderstood by many people.
Once Carl has a good understanding of the basic system he can start to look at the differences between VM's.
Thats all for now, I'm off to bed.
Modern cars, Its all wizardry and witchcraft