My reasoning is this. If I publish something, and claim copyright on it '(c) yyyy' for example. Then, after yyyy+a years it could be known by all to be copyright free, because you have the original published document in your hand which states the start date and the term is known. With the possible +b included, it becomes difficult to determine what the copyright status is because you don't know if it has been 'extended' so you really need to wait until after yyyy+a+b. With the current system of life+b then its even harder to know if a published work is out of copyright unless the author is well known, and because this suits the entrenched interests I believe that it is at least partially intentional.
If pirate parties or anybody else want to campaign for copyright reform, then my utmost wish would be that they fix this issue at the start. Lets have a fixed term please.
The main principle is just that if you no longer care about something enough to do a little work to keep it, then the time has come to release the rights to that thing into the public domain. A bit of paperwork every ten years may be good enough for that.
Registration could also clarify ownership. Problems like what happened with NoLF [1] or Google Books might be less likely.
[1] http://kotaku.com/the-sad-story-behind-a-dead-pc-game-that-c...
This will have to be fixed before China can start producing its own export-quality cultural products.
It's yet another case of a motivated special interest.
[1] http://www.theguardian.com/media/2011/sep/12/musicians-copyr...