absolute coordinates on svg paths

Hi all,

For long I've been using svg and have developed some translation tools for
free CAD/CAE design applications.

Theres a thing I've never understood, and it is why you can't specify
absolute units like cm or in to SVG paths?. Is there any implementation
reason? or Is it planned to include it in future releases of SVG specs?

Googling I've found it is no only my problem, there are others suffering the
same :)
http://lists.freedesktop.org/archives/cairo/2005-June/004390.html

Thanks!
José Ignacio Villar.