The Debian developers split the distro into categories based on stability: stable, testing, unstable and sometimes even experiemental. Debian stable is what it is: old working stable programs. Debian testing is the testing & proving grounds for the next stable release. Debian unstable is where new and untested packages get inserted into the distro. Experimental in mostly unoffical and usually not supported. So thats what the categories are.

Why is Debian stable so out of date? Debian developers must coordinate a MEGA release for about tested 9000 packages across a wide variety of platforms: i386 (386,486,pentium,p2,p3,p4,celeron,xeon), ia64 (itanium), alpha (dec alpha), sparc (sun microsystems), arm (StrongARM), amiga, s390 (IBM Mainframe), x86_64 (amd & intel 64bit), hppa (HP PA RISC), m68k (Motorola 68000). This is a huge undertaking and they about a year late. Hopefully in a month Debian testing will become Debian stable and we (the community at large) will get a good known working Debian system.

So how does Knoppix stay up to date? Knoppix pulls its packages from multiple categories (stable, testing, unstable) to make a working up to date system.