Arch Linux

That sounds like a feature request. Deluge doesnt require the libtorrent library to run. The library is not even in extra.
Not even the upstream provided deluge.PKGBUILD has it listed as a dependency. http://download.deluge-torrent.org/arch/1.1.2/deluge-1.1.2.pkgbuild
Debian does it is not a reason for everyone else to do it

Well, deluge needs libtorrent-rasterbar! Just look into the sources...
They have it in their own source tree because big distros (like debian) didn't had a package for that. Debian has a package for libtorrent-rasterbar now - so there is no need to build the included library in deluge. ;-)

http://dev.deluge-torrent.org/browser/trunk/libtorrent

By the way... I didn't say that "debian" is a reason. ;-)
It's only a hint that it is possible to switch from internal library to system library!

A little example:
I rebuild libtorrent-rasterbar 0.14.2 with --enable-python-binding and link deluge against it instead of building included lib.

deluge package:
Installed Size: 16143,00 K (included lib)
Installed Size: 9852.00 K (use rasterbar package)

And updating deluge is much more faster now because it only needs to byte-compile the python scripts.

Just in case there could still be some confusion, the first line of Deluge's About web page is quite clear :
http://dev.deluge-torrent.org/wiki/About
Deluge is a full-featured BitTorrent client for Linux, Unix and Windows. It uses libtorrent in it's backend and PyGTK for it's user interface.
And libtorrent links to http://www.rasterbar.com/products/libtorrent/

Though it might be problematic that deluge is maintained in extra, and libtorrent-rasterbar in community.
To make things worse, both arch packages are also out-of-date.

To Misery : it could still be helpful if you could provide patches for these two pkgbuilds, for implementing your feature request.

Xaviar: there is no big patch needed. libtorrent-rasterbar only needs --enable-python-binding in ./configure and deluge needs libtorrent-rasterbar>=0.14.2 as depends(). The build system of deluge will detect the system lib and will use it. :-)

Ok perfect, that is simple enough, thanks for the clarification.

I will try to move this to [extra] and update both packages (deluge and libtorrent-rasterbar).

I saw that discussion about to rename that package to libtorrent. I don't think that it is a good idea because every other big distribution uses "-rasterbar" for this library and "libtorrent" for rakshasa.

And the library itself uses that name, too:
$ cat $srcdir/libtorrent-rasterbar.pc
[...]
package=libtorrent-rasterbar

Name: libtorrent-rasterbar
Description: Bittorrent library.
Version: 0.14.2
Libs: -L${libdir} -ltorrent-rasterbar
[...]

Fixed on deluge 1.1.5.