APT needs a patch to become free-software-friendly (confirmed at least for Trisquel 4.5, 5.5)

cat /apt-0.8.3ubuntu7trisquel1/doc/examples/sources.list

# See sources.list(5) for more information, especialy
# Remember that you can only use http, ftp or file URIs
# CDROMs are managed through the apt-cdrom tool.
deb http://us.archive.ubuntu.com/ubuntu hardy main restricted
deb-src http://us.archive.ubuntu.com/ubuntu hardy main restricted

deb http://security.ubuntu.com/ubuntu hardy-security main restricted
deb-src http://security.ubuntu.com/ubuntu hardy-security main restricted

deb http://us.archive.ubuntu.com/ubuntu hardy-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu hardy-updates main restricted

Upstream bug : https://savannah.nongnu.org/bugs/index.php?29724
http://libreplanet.org/wiki/List_of_software_that_does_not_respect_the_Free_System_Distribution_Guidelines#apt