Modules vs. components in Joomla?

Was just flipping through some easy to read stuff on Php-Nuke modules in the book Php Nuke Garage. Joomla components sure seem similar to Php Nuke modules, the way they take those HTTP POST values from the Apache server:

http://joomla/index.php?module=mymodule&op=one

Do a switch statement on them, and then execute something. Same basic structure. Well from the Joomla! glossary:


Modules:

1. Extend the capabilities of Joomla! giving the software new functionality.
2. Are small content items that can be displayed anywhere that your template allows it to be displayed.
3. Include: Main Menu, Top menu, Template Chooser, Polls, Newsflash, Hit Counter, etc.

Components:

1. Are Joomla!’s content elements or applications that are usually displayed in the center of the main content area of a template.
2. Depend on the design of the template in use.
3. Are core elements of Joomla!’s functionality.
4. Include Banners, Contact, News Feeds, Polls and Web Links.

So modules are minor things that go in the left and right sidebars of a three column layout and components are major things that go in the center? The plot thickens. I'll find out tommorrow!