The VL sources are hosted, but I'm not sure we would be required to host the actual Slackware sources used. That would be the responsibility of the Slackware folks.
You didn't read the article did you

?
because MEPIS has not previously supplied source code for the packages already available from the distribution it is based on -- once Debian, and now Ubuntu -- it is in violation of the GNU General Public License (GPL).
The GPL is pretty clear about it as well:
3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:
a) Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,
b) Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,
c) Accompany it with the information you received as to the offer
to distribute corresponding source code. (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)
The source code for a work means the preferred form of the work for
making modifications to it. For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable. However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.
If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.
So, if you host packages, you must also host the sourcecode and buildscripts etc.
Probably there is a good reason for this, which is scaping from me, but I dont see the need of multiplicate the same source in all the www...
The idea is, that if one source is lost (for instance the official site is hacked / closed), you can still find it elsewhere. For instance, I had a hell of a time trying to find some sources that used to be hosted on
www.plugin.org.uk when that site was down. Thanks to this clause, I could still find it elsewhere.
If Linux distributions don't even follow the GPL, then why should others?