Greetz (you just knew I'd show up, didn't you
It is not so simple as to assume Slackware full release is like Debian Stable or that Current is like Unstable/Experimental. One of the beauties of Slackware is that it is not a committee system being one designed by a very small team with one man, Patrick Volkerding (whom you can contact directly btw) as final God arbiter. Packages are chosen for Slackware not because they are new or old but because they work.
Here are two examples:
On a lower level and as an example of how changes in a program to better suit a particular distro or set of libraries can ruin function in another is Checkinstall. This used to be an awsome little utility that would build RPMs, Debs, or Slackpack TGZs from source so that they could be installed by the local installer and be available for uninstall tracking as well. When a new version ruined it's compatibility, for a time the older version was what was bundled with Slackware with a note that if and when it was fixed, an update would be available. It was never fixed so it was dropped and later sort of replaced. or more accurately made kind of obsolete by Slackbuilds.
On a much deeper level, several years ago, a new GCC came out and was apparently "served before it's time" and Red Hat and Debian Experimental went crazy, backpedalling and patching. Slackware Current moved up one jump to a still stable GCC instead of 2 jumps to newest and explained that it had been tested and found wanting.
Lately Eric Hameleer has become a powerful force in Slackware and his blog details what Current is all about on an ongoing basis, since he is largely responsible for so much of it anymore, being the designer of Slackware 64 among many other achievements. It can be found here where there are also links to Slackbuilds for which he is a major contributor. Both Eric and Patrick routinely post (and answer posts) on the Linuxquestions.org Slackware section.
An extremely useful mirror (and all around amazing website and friend I met on IRC) is Alphageek, here
Hope you find these useful and enlightening