The Problems of the Public Domain
Here's an interesting exploration of the perils of putting your stuff into the public domain:Countries with moral rights protections, the right of the artist to be attributed for their work among other elements, often make those rights inalienable, meaning they can not be given away under any circumstance.
Therefore, in these countries attribution rights still rest with the respective authors and these dedications are little more than a promise not to sue if those rights are infringed. That is a promise that can be revoked at any time.
Second, there are some theories that hold that putting a work in the public domain might be seen as a gift and not a legal agreement. If such a gift were found to be an “unenforceable promise”, it could be retracted at a later date.
Third, the posts themselves were not written by attorneys and are very informal in nature. Though Creative Commons has a public domain dedication system, they both chose not to use it. It remains to be seen how these dedications would hold up in court if ever they were challenged.
Finally, the dedications only extend to existing works. The authors reserve the right in the future to reserve some or all rights in newer works. This could be seen as a block on activities such as scraping that are ongoing and automatic.
So while the dedications certainly are intended to forfeit all copyright protections on their work, they do not do so completely because it is impossible to do so.
Copyright law resists the public domain and favors automatic protection. This frustrates many in the field, but it is the nature of the beast.
The whole post is quite long, but it's well worth a read for the interesting perspective it puts on the public domain. (Via P2P Foundation.)