One comment and possible explanations for Noda's victory in answer to Peter Cave's good question:

Comment: the outcome should put to rest (I hope) the notion that the factions are these disciplined, cohesive bodies like the LDP's used to be pre-1994.
Although we need to await a deeper analysis by the media of who voted for whom, my bet is that Noda's victory may have came out to a simple pro- vs.
anti-Ozawa bias.

And this brings me to Peter's question:

First, parties of course are not unitary actors so they don't "think" collectively so therefore hard to say what the motivations of different individuals were. But if there were incentives shared by enough people to vote in Noda, they might fall into the following
categories:

a)as above, desire to keep Ozawa's favored and supported candidate out because they want to decrease Ozawa's influence and prove to the public they are not the unpopular Ozawa stooges.
b)a rational strategy for next election: let the conservative Noda raise taxes and try to come to consensus with LDP for a year; if he fails or succeeds but either way proves (as is likely) unpopular, then bring in Maehara before the next election (i.e., consider Noda a temporary leader) c)variation of a) and b)show the public they are not in Ozawa's pocket, let the legal process take its course and maybe get rid of Ozawa, then have a new election where they can pick someone more popular with the public d)deeply rooted death wish by a party that can't get its act together and doesn't seem to know how to govern.

Best regards, Ellis
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Ellis S. Krauss
Professor, School of International Relations and Pacific Studies University of California, San Diego La Jolla, CA 92093-0519
Tel: Contact via email is better
Fax (home): +1 (760) 943-8881