PageMaker was based on the idea of physical paste-up. You grab an image or piece of text and place it. Each article is an atomic piece. Everything else I've seen starts with the idea of a single document, and you're just changing formatting.
Think of using something like Word, but everything is a text box or image box. And the tools are designed to work with them that way. Also, for multiple columns you can grab the continuation widget from the bottom of one column and continue that piece of text on another page.
It really addresses the difference between one person making one document, and one person assembling the output of several people into a larger work.