IPCop could very well be developed as an add-on to an operating system in the way that Shorewall is an application to be installed on a Linux system or ISA server on a Windows system, making it an application you install over your existing setup. You would then be left with the maintenance of the system underlying the software package.
The disadvantage of this is that if your server's purpose is only to be a firewall for your network you would be required to have an adequate basic understanding of the Linux operating system in order to get the software installed and if you want it to perform well you would have to configure both the operating system and IPCop itself. However, since IPCop installs as an operating system of its own, you have no real need to know Linux in order to use the system. When it comes to stability, this means that the IPCop developers can concentrate on one platform for their development and can be completely confident...