PROFESSOR BAINBRIDGE has an item on "self-plagiarism" in law reviews. You can read my views on plagiarism in this chapter from the ethics book I wrote with Peter Morgan. But the short version is that I don't think that there's any such thing as "self-plagiarism." Plagiarism consists in passing off someone else's words as one's own, so you can't self-plagiarize. (Arthur Leff, one of my scholarly heroes, had one passage he repeated in almost everything he wrote. But it always worked. Why change perfection?)
At any rate, like many issues, this is better dealt with by contract than by rule. If law reviews think that too much work they get is repetitive and unoriginal, they're entirely free to require that no part of any work they publish can have been published before. Problem solved, if problem it is.