I think the point mluiten is making is that you have to actually create the content (or pay someone to create it) to have copyright, whereas you don't have to implement anything to have a patent granted. Since content creation is much more expensive than content distribution, there would be no economic incentives for "copyright trolls."
Actually there are lots of copyright trolls, especially in the cases where the content is cheap to make (as in time invested) and cheap to distribute -- like news articles, music or photography.
Say you've got a popular photo, you can transfer the litigious rights of it to a copyright troll and that troll will then sue everyone using it.
Copyrights are indeed transferable. In fact, many of the most well-known free software projects rely on this fact (e.g., should they want to relicense, or to make it easier to defend copyright ownership in court by having a single legal entity behind it).