I've seen some law review articles that get into these issues.
The better argument is that its NOT a derivative work when you open a web page. There is no "copy" involved since you simply display the portions of the web page you wish, and leave out those you do not want to see.
Sort of like reading a book, but skipping the intro, and flap cover.
They can't sue you for not reading something.
The attack against the software that blocks the add is the best shot but any suit against an end user would flop.
The only way it would work is if the ad blocker was installed and working without the knowledge and consent of the end user. A well written TOU policy will pretty much mean a great big fuckyou to the internet advertisement industry. About time...