They definitely mean selinux. There only needs to be a single issue for an average user to disable selinux.
I thought selinux was available as a package on non-RH distros, but install it and enabling was very painful unless you are an selinux expert, so almost no one on those distros does.
Are you sure you don't mean AppArmor?
I think they did mean selinux. You are absolutely right that nowadays it just works for the most part. The big exception is for people deploying applications that don't have selinux config shipped by Red hat. Those people have to configure things properly, and rarely do people bother. If you do things like change the default ports for services, that can also get you in selinux trouble.