Well, apparently the chip does
something.
Thread 1
See Eddie Gilmartin's post in this thread, as well as Lightman's post below it explaining how the chips work in a Diesel.
Thread 2
(Edit)By the way, my diesels don't have throttle plates. But my E300 does have an electronically controlled turbo wastegate and EGR valve, which can certainly have an effect on performance. I haven't dug under the intake manifold to take a peek at the injection pump yet.