vignettes: problems with PDF compaction

[Env: OS: Win Xp; R 2.15.2; IDE: eclipse/StatET]

Each time I update my heplots package, I get warnings from R CMD check
on R-Forge,

* checking sizes of PDF files under ?inst/doc? ... WARNING
   ?gs+qpdf? made some significant size reductions:
      compacted ?HE-examples.pdf? from 739Kb to 366Kb

To follow up my own post, I did some more checking of whether/how to
compact PDFs on my own system.  My conclusion is that that I am unable
to comply with the request from CRAN maintainers, even though I would
like to.  Once again, I wonder why this cannot be handled on the CRAN
side automatically.

qpdf: running it from a cmd prompt (using the options from 
tools::compactPDF) doesn't do very much compression

C:\R\test>qpdf --stream-data=compress --object-streams=generate 
HE-examples.pdf
HE-examples-comp.pdf

C:\R\test>dir HE-examples*
04/22/2013  10:55 AM           699,191 HE-examples-comp.pdf
04/22/2013  10:28 AM           756,624 HE-examples.pdf

gs:  I have gs installed at C:\Program Files\gs\gs9.07\bin\gswin32.exe,
but the gs installer doesn't put itself on the path, so 
tools::compactPDF sees gs_cmd as empty:

 > gs_cmd = Sys.getenv("R_GSCMD", "")
[1] ""

so it can't run gs+qpdf.  OK, so I try to do it manually:

 > Sys.setenv(R_GSCMD = "C:/Program Files/gs/gs9.07/bin/gswin32.exe")
 > setwd("test")
 >
 > tools::compactPDF("HE-examples.pdf")
 > tools::compactPDF("HE-examples.pdf", gs_quality="ebook")

But this doesn't do anything, not even changing the timestamp on the 
file, because the file size doesn't change enough.

C:\R\test>dir HE-examples.pdf
04/22/2013  10:28 AM           756,624 HE-examples.pdf

Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University      Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street    Web:   http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA