I guess I'm wandering away from the topic here (since the current issue seems more related to contract law than to the ethics of plagiarism)... but I'm not sure it's so cut-and-dried a definition. Plenty of people and academic authorities include the uncredited appropriation of
ideas in their definition of plagiarism, not just the wholesale lifting of entire passages/works word-for-word.
e.g. Harvard's "What constitutes plagiarism" at http://isites.harvard.edu/icb/icb.do?keyword=k70847&pageid=i... says:
"[I]t is considered plagiarism to draw any idea or any language from someone else without adequately crediting that source ... When you use your own language to describe someone else's idea, that idea still belongs to the author of the original material. Whenever you use ideas that you did not think up yourself, you need to give credit to the source in which you found them, whether you quote directly from that material or provide a responsible paraphrase."
Wikipedia and the dictionary on my Mac also make reference to the taking of ideas as plagiarism, so it doesn't seem uncommon to include ideas in the definition.
EDIT: markdown fail.