You are totally right that some of the parked domains make a lot of money. For example, Anything.com Ltd. owns a slew of domains (look at marketing.com) which

You are totally right that some of the parked domains make a lot of money. For example, Anything.com Ltd. owns a slew of domains (look at marketing.com) which are nearly all parked. They make money from users clicking through and I'm sure they earn a lot of money, but imagine how much more they could make if, at minimum, they created a better affiliate site that didn't look like a crappy parked domain. Even if they just changed the design and kept basically the same strategy, they could probably double their money. Frankly I'm amazed they don't try harder. How many people actually click through the links on a parked page? Personally I hate these pages and immediately close them. If they just put in the effort to create a "real" site, they would draw in a much higher percentage of users. It may not be the case with Anything.com Ltd., but I'm sure that there are many domain owners who don't have the knowledge or resources to make a decent site. So, if they paired with a competent developer, they greatly increase their chances for success.