Selenium IDE is a Record and Playback tool, but it is not reliable. As web applications are frequently changed, the IDE is not a good solution for a production environment.
Suppose you record your test, and you find an element with a dynamic ID. Sure we can import it into eclipse, but what happens when that test starts failing? why not simply make your test agile and independent to catch these in the first place.
So IDE is designed to be a quick solution to automation, but it is not a solution to a full regression suite.