SELinux is on in Fedora, but not in other linux distributions. This does not mean that they are less ecure. SELinux makes some assumptions for a linux system that prevents ISPConfig on running.
If you want to have a really secure webserver i recommend not to install PHP or perl or any other scripting language for webpages as most hacks currently are done trough unsecure scripts. Then do not install any management software except an SSH server on a non common port and remove all compilers from your system.