Debian may have started out as a typical Linux distribution, but it is more than that now. Other distributions, especially commercial distributions like Red Hat and SUSE, still tend to treat their Linux distribution like more traditional software products. Raw materials, in the form of software from Free / Open Source projects, goes into a black box where it is packaged and prepared by the vendor and comes out as if under cellophane. The companies may provide the source code to their packages, but they lock up their build and distribution processes tight. They trade the complexity of the build, quality assurance and distribution processes in exchange for money. The upside for their customers; simpler access to Linux. The downside for their customers; dependency on the distribution provider for new technology, quality control and ongoing support.
Debian is a different when compared to other distributions. One way to show this difference is to say that Debian is to Linux distributions as McDonalds is to hamburgers. McDonalds will certainly sell you a hamburger, but it is also possible for McDonalds to teach you how to franchise their restaurant and make burgers yourself. So while you can certainly get a Debian GNU/Linux distribution, the hidden value of Debian is actually in learning how to make and control your own operating system using Debian's experience and tools.
The Power Of Franchises
The reason the distributions like MEPIS, Linspire, Knoppix and Ubuntu are based on the Debian architecture is largely because of the availability of the specialized tools and knowledge Debian has accumulated showing how to build, test, and distribute its operating system. The developers in those franchise projects are using and improving Debian's processes and some are even feeding their experiences back to the Debian Project and improving things for all the other franchisees.
All the people involved in those projects are learning the Debian distribution architecture and how the Debian development tools work. I believe this is one of the most understated threats to the business model of companies like Red Hat and Novell. Just like Linux itself, when a community forms to commodify a technology segment, competition really heats up and the price drops through the floor. The only real advantage commercial distributions currently offer over community / franchise distributions is a slightly more conventional vendor relationship and security/ISV certifications. While I admit those are valuable differentiators in certain market segments, their long term value will be eroded by improvements in both Debian and the franchisees making Debian-based distributions.
Debian in the Real World
There have already been press stories and Linux user group anecdotes about how the Department of Energy first used Red Hat and was unsatisfied with the support and the costs, then when they tried SUSE, SUSE actually lost the source code to the DoE's customized cluster kernel. The DoE finally settled on leveraging Debian and doing things in house. The reason the the City of Munich picked Debian was not necessarily because the Debian GNU/Linux version Sarge was so much better than any of the other distributions, but because the software and distribution process is visible, available and extensible. I fully expect to see many more stories about people leveraging the experience and maturity in the Debian process to allow them to bring the distribution maintenance inside their IT department.
Let me give you an example from my company. We use Linux on the desktop for the whole company. About four years ago we created a mirror of the Debian Unstable repository on our local network and rolled out a client configuration based on it. When a major software update hits Debian Unstable and we decide to install it on our clients (such as OpenOffice.org or KDE updates) we sync back up to the Debian Unstable repository, test an upgrade on a couple of clients, work out any kinks in the process and then 'apt-get update ; apt-get upgrade' the whole office.
This configuration control now also extends to automating the installation process. The new Debian installer is very easy to automate. I have developed a preseeded client installation which allows me to hook a blank PC up to the network and boot off the network to load our custom configuration. So if someone really kills their box somehow, they can reboot their PC, hit [F12] during the POST to boot from the network, and go to a meeting or lunch. When they come back their PC is waiting for them to login and start working again.
This kind of experience working with the Debian architecture and installer has been beneficial to Debian as well. I've been able to give technology improvements back to Debian in the bug reports with patches for the packages we use, new Xfree86/Xorg drivers for a previously unsupported touchscreen input device and a much faster, perl-based hotplug system.
Control is Money
So when you hear about Debian or one of the popular Debian-based franchises, keep in mind that Debian is different from other GNU/Linux distributions. Debian enables anyone to support themselves if they are willing to spend a little time and effort. Using the Debian architecture gives ultimate control over the operating system and deployed software. That translates to control over the decisions about if and when to upgrade. And as Microsoft so aptly demonstrates every quarter, that control is worth a great deal of money.