It's an interesting model that has evolved considerably.
They run a website called http://www.webscriptions.net where there is also a link to the Free Library, where you can get books for free as well. The point here is that they are mostly first or second books in a series; they try and get you hooked so you buy the sequels.
Other publishers have started to make some of their works available via webscriptions as well. The price point is usually considerably cheaper than buying the dead-tree equivalent.
An alternate model that magazines may look at (if they have not already) is lulu.com; publishing on demand for outdated / back-issue content could work, given they already have the logistics tail in place…]]>