Copyright: the Idea/Expression dichotomy

In the early twentieth century copyright in the US (and this had a strong influence elsewhere) took an interesteing turn. The publisher of General Wallace's book Ben Hur sued the film production company that made a silent movie of the same name with a similar story. They claimed that this was a "derivative work". The courts concurred and thus destroyed much of the idea/expression dichotomy, which is that copyright only exists in the specific expression of an idea and not in the ideas themselves.

Random House, the publisher of Dan Brown's book "The Da Vinci Code" is being sued by the authors of "The Holy Blood and the Holy Grail", a historical conspiracy theory book (it's hard to know whether to call such things factual books since they're quite rife with speculation, but maybe the term non-fiction is the best way to describe it). They're claiming that the central premise of the Da Vince Code is drawn from their book and as such it is a derivative wok and they deserve recognition and payment. The publisher is claiming that this violates the idea/expression dichotomy and that Dan Brown researched many sources with similar ideas before writing his book - copying from one source is plagiarism, copying from many is research. Of course as a piece of fiction rather than non-fiction the Da Vince Code probably (I haven't read it) doesn't list references that way a piece of scholarly (or pseudo-scholarly such as HB&HG) work would.

So, is Random House being hoist by the petard of Harper Brothers here? Unfortunately, Random House and Harpers are not, to my knowledge, part of the same conglomerate, thereby deying a certain amount of irony. Pity, that.