Why are package managers tied to distributions. Porteus (http://www.porteus.org), a little known slackware based distribution, has a package manager which can download and install packages (with dependencies) from both Slackware and Debian repositories! A package manager which can be installed in any distribution and which can download and install packages from any repository will be an instant hit.

It will rather be a guarantee for instant breakage. Distros usually are not very compatible, even if you look at Ubuntu and Debian, which use the same package format and managers, mixing repositories is a very bad idea. Now mix Arch, Fedora, RHEL/CentOS/SL, Mandriva, Mageia, Slackware and whatnot into that and you will have an unusable system.

And a vehicle that was an aircraft, automobile and submarine all in one would also be an instant hit. I wonder which one would be easier to make?

On one hand you are saying that Slackware is good because it allows one to install applications from other sources. On the other hand, you don't like a package manager to install from multiple sources. Moreover, tools are available for converting packages between deb, rpm, tgz etc. So why a package manager should not use such methods to install software from multiple sources? Such a package manager will be a boon to smaller linux distributions that do not have their own repository. Installation from Debian repositories is possible in Puppy linux also (http://puppylinux.org/wikka/Debianization).

Indeed, if those sources are Slackware repositories or repositories that are compatible to Slackware, like the Salix repository.

This has nothing to do if I like it or not. This is a technical question. Different distributions are not necessarily compatible, even if they are very close together. Debian is not compatible to Ubuntu, and even closer together, Backtrack is also not compatible to Ubuntu (and Debian, FWIW), despite the fact that all three use the same package format and the same package management system. Mixing them will break your system, there is no way around this.
Those tools make a "dumb" conversion of single packages. If a converted package is not binary compatible with your distribution changing the package format will not change that, you need to recompile from source to make it binary compatible and even that is not always possible, in regards to different versions of the same software with different dependencies.

As stated above, because such a package manager will break your system.

If the distro supports Debian packages this is possible. This was not the case for Puppy 4 (for which the link is meant that you provided), but in some cases it worked. Note the warning on the linked page:In other words: This procedure may break your system. Newer versions of Puppy come in different flavors, like Lupu (compatible to Ubuntu) or Slacko (compatible to Slackware). You can not install Slacko packages in Lupu and the other way around. Well actually you can, but their is a) no guarantee that the installed package works and b) no guarantee that your system behaves correctly after the install.

If a distro has no own repository because of the lack of manpower or infrastructure there is a simple solution: They can use the repository of their parent distro, since those distributions usually are not independently created.

What I do and do not like is irrelevant. This is a matter of reality. Distributions tailor packages to be compatible with their specific systems. And that is in addition to there being three main packaging formats, along with a few unique to single distros. A single package manager that could install anything from any source would need to be incredibly complex. Not only would it need the ability to convert .deb, rmp, .targz and Arch formats, it would also need the ability to modify packages from any other system. (Modifying an Ubuntu package into a Debian package for instance.) Such a utility would require an huge amount of effort from developers of every distro working in co-operation toward a common goal. It is unlikely resources will be diverted away from maintaining distros to create a magical package manager that almost no one feels a need for. It would be nice, but then so would world peace. (World peace will probably arrive before a single Linux package manager.)

EDIT
TobiSGD beat me to it, but I shall leave the post intact, because it took a few minutes worth of effort to type.

Package management is certainly one aspect of Linux that is confusing to new users, as it is handled differently by each distro. Each has its pros and cons. Additionally, however, it is possible in any distro to compile software and install from the source.

Distrowatch has a good run-down on the various package managers:

http://distrowatch.com/dwres.php?res...age-management

The only thing I would add to JW's post is some people new to Linux fail to understand that Linux is not a single system with many flavours, but rather, every distribution is a unique system built on top of the same kernel.

Which is the best method/distribution/tool if one wants to install software only from sources (tar.gz) downloaded from individual software websites (i.e. not using linux distribution repositories at all)?

Try Linux From Scratch.

I am not interested in compiling system software. I am thinking of installing a basic install of slackware/arch linux and then for various user applications I stick to downloading sources from software's websites and compiling them. What problems are likely to be there in this approach?

There really shouldn't be a problem, as long as you know how to compile, and understand the Linux file system.

Use one of the stable distros, like CentOS, Debian or Slackware. This way you won't have problems with your self-compiled software when the underlying libraries change (something that would be much more likely with Arch), since the package manager doesn't know anything about your self-compiled software. Actually, this is usually what you do with Slackware anyways, if you don't want to use third party repositories, just that you use a script for compiling the software which also automatically builds a package for your system, so that uninstalling and upgrading the software is a much cleaner process.

I have a long unused slackware-13 with KDE installed on a partion. It boots but how can I update it? There are steps mentioned on this page ( http://distrowatch.com/weekly.php?is...090518&mode=66 ) which will make it to slackware-current. Is this a good idea? Later I want to install software from sources.

You can update your Slackware 13 installation by uncommenting one of the servers in the mirrors file (should be for version 13):

/etc/slackpkg/mirrors

After that:

The directions for switching to current on that link looks legit.