Ritchie - I take your point and I'm happy to answer as best I can, but I'd note that I'm not a lawyer and so am unlikely to be able to give as definitive answers as the ones that have already been given over the past few years on legal-talk and elsewhere. But anyway...
If you're into contract law, then there can't be a contract without "consideration".
On that specific point, I will indeed quote a lawyer on OSM legal-talk:
There has to be consideration, but if I say to you - if you want to use my data you must agree to abide by these contractual terms - then there will be consideration: you get the use of the data, and I get whatever I get out of the terms and conditions (eg you agreement to do or not to do certain things). Contracts very rarely fail for want of consideration. NB: this is all in English law terms, other systems of contract law work differently.
If an individual fact cannot be copyrighted, and it is not held as a trade secret, it's in the public domain, surely? Some countries allow aggregated facts (ie. a database) to be copyrighted, many don't.
The only way the GPL or CC work is that copyright law is more restrictive, and licensing rights are unilaterally granted by the copyright holder.
Yes, indeed. But you can't magically make a database of facts copyrighted by applying a copyright-based licence (such as GPL or the unported CC licences) to it. It's right there in the CC preamble: "Work means the copyrightable work of authorship offered under the terms of this License."
If it's not copyrightable, then the CC licences don't offer any protection. Creative Commons itself has in the past recommended against using its copyright-based licences for factual databases. The OSM community formed the view, though not unilaterally, that a share-alike licence with a higher probability of enforcement (via copyright, database right and contract) was preferable. Hence the move to the ODbL. No-one has claimed that it is guaranteed to enforce share-alike and attribution in 100% of cases, but the probability is very significantly higher than a copyright-only licence.