I think what they do is find a common mis-type of a popular domain (like AmOzon.com instead of Amazon.com) I'm not sure if parking regular domains would make very much money. I think it is mostly an option for people who have a website, but can't put in the time and effort to run it anymore, but they still want SOME income to come from that unused traffic.
I'm no expert, but I would think you'd make more money off them if you just bought 10 articles for each one, put some Clickbank or Amazon product links in there, and bought an autopilot SEO service package. Then after they're ranking a little bit, sell them.