Ok, first thing to understand here is to take a look at how Google regards subdomains - see the video attached.
I heard before, that the difference is that when you have a subdirectory, then the pages in that subdirectory count towards the overall authority of your main domain, whereas if you have a lot of subdomains, they are regarded by Google as separate websites, not connected to your main host.
However, I believe that by using the strange URL structure they are using:
http://silverleaf-resorts.pissedconsumer.com/complaints.html
they are making a connection between the subdomain and the page on some level that Google recognizes as a signal to put it all together. This is just a guess.
Another thing to pay attention here is that when they use
http://silverleaf-resorts.pissedconsumer.com/
the key phrase "silverleaf resorts" is placed right at the beginning of the URL, which in my opinion influences the position in search results.
matt-cutts-talks-subdomains-vs-subdirectories-2012-10