LR4 book module: Exporting book as PDF when book type is set to 'Blurb' (rather than PDF) does not use the 'Blurb' quality parameters (e.g. colour space, jpg compression) but instead uses values from previous adjustments when book type was set to PDF.
example: 1. With Blurb selected I exported a PDF using the button on the left hand panel.
2. I changed from Blurb to PDF and dropped the jpg quality and ppi to low values. I exported another PDF and as expected, the file size and image quality where noticeably smaller / worse.
3. I then changed back to the Blurb option in the book settings panel and I exported a third PDF. I expected this to match the first PDF in terms of file size and quality, but in fact this PDF was still small and crappy like the PDF from step 2.