Concur. It is an immensely useful tool, simple as it may be to set up. There are services that do it for you (getexceptional), but it literally takes only a few hours to throw your own together.

Issue tracking is probably moving too much into management territory for this list, which is why I think they left it out.

It's probably for the same reasons that they don't touch upon server management/configuration, but I have personally found puppet (or other similar tool) very useful. It's basically source control for your server configuration - once you start using it, it seems reckless to not have.