PageRank™ - Google's original secret sauce has truly shaped the way the web looks. Now, people build whole domains to acquire PageRank - because it's very valuable stuff.
The author of the page is probably just a hacker who thought it was a cool idea to create a whole domain as a mini-reference.
On the other hand, he includes a bunch of "digg this" type links at the bottom - great for acquiring PageRank. His domain currently has a PageRank of 5.
Eventually, this page could be useful for other SEO purposes. I wonder if that's partly why he built it.
As another example, look at Aaron Wall's SEO for Firefox extension. Aaron is doing a good thing for all the SEO's out there providing this free tool. And in return, he could increase his PageRank - or at least have better organic search rankings and acquire more traffic.
Since PageRank (or more accurately, Google's overall trust assigned to a page or domain) is easily monetized by SEO's, it creates an economy that shapes the web.