The article is pretty clearly written for someone who is already an emacs+org user. I guess it was posted mostly as a teaser of what can be done with it.

The "plain text" catch phrase is not baseless, though. One of the best things about org mode is that there really is a simple and intuitive markup format at its core. Most users probably only ever use the "outliner" features, which are pretty obvious. But once you're used to that, there are lots of more complex features you can start using, one by one. Or just ignore.

Being text, org mode files are also pretty easy to e.g. grep.