Why is DPI parameter not having effect when printing a PDF document?

Q: Our problem:

We took your examplcode from http://www.pdftron.com/net/samplecode/PDFPrint.cs
--> works fine

Then we changed the dpi to 72 (from 300) :

But printed output is having the same quality as before (300DPI).
Why is DPI parameter not having effect when printing a PDF document?
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A: What is the rasterizer that you are using? If you are using
e_GDIPlus rasterizer you will not notice any difference in print
quality because the data is sent in the vector form. On the other hand
if you switch to e_Builtin rasterizer, or if you change 'example'
variable (in the sample code to) to 1, you should notice the effect of
the DPI parameter.