To Translate somewhat,
Long Term Support is relatable to how long you can use Ubuntu Repository Sources
If these sources are offline, you can no longer apt-get, now you can upgrade the distribution, which will change these sources, but you may have issues if you do not remove any added repositories, and it is usually advised to start with a fresh install.
You will see mention of this because 10.04 and 10.10 were previous to the introduction of Gnome 3/Unity, so when you did a dist-upgrade to 11.04, horrible things happened, most notably the loss of Gnome 2.
You can run without the repository and maintain an older version by compiling from source.
Systems that are not so dependant on running the latest desktops and applications(servers) are not as affected.