I am having the same problem. Also felt like i'm the only one with it.
I'm using dwf with the publish in autoCAD 2010. The same file with the same ctb plot nicely with our xerox or direcly in PDF using autoCAD PDF plotter.
No, even at the same size - half (c) or full (e), the pdfs come out slightly darker and dwf comes out even more dark. As there is no way to choose the pc3 on these plot formats, I'm open to suggestions (besided plotting from color) on how to make these pdf/dwf plots come out light.