Resulting document size when Including a graphics file multiple times - pgf vs. graphicx

In his answer to the question Tikz: using external images as building blocks. Stefan Kottwitz says:

The pgf way may be preferred if the document size matters and graphics are multiply used or if masking is desired.

When is there a problem regarding large document size caused be multiple inclusions of the same image? With a random photo in jpg-format I get the results below using the following test-files:

\documentclass{article}
\usepackage{graphicx}
\pagestyle{empty}
\begin{document}

\newcount\n
\n=0
\includegraphics[width=5cm]{IMG_1823.JPG}
\newpage
\repeat

\end{document}


and

\documentclass{article}
\usepackage{pgf}
\pgfdeclareimage[width=5cm]{test}{IMG_1823.JPG}
\pagestyle{empty}
\begin{document}

\newcount\n
\n=0
\pgfuseimage{test}
\newpage
\repeat

\end{document}


Compiling with pdfTeX-1.40.10 the resulting document sizes are (output from pdfinfo):

pgf-version:
File size:      1673589 bytes

Graphicx-version:
File size:      1667806 bytes


The photo is about 1.6 Mb:

\$ du IMG_1823.JPG
1592    IMG_1823.JPG


Adding \pdfcompresslevel=0 and inspecting the contents of the pdf-file directly both methods seem (as far as I can tell) to embed the image data once only?

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