Since Len Schoppa invoked Ramseyer/Rosenbluth on behalf of the notion that material interests dominate rational choice thinking, let me jump in here for a minute. There is a substantial body of "rational choice" literature on the value of ideology as a sorting device, both for voters and for politicians. See, for example, work by Jon Elster, Gary Cox's EFFICIENT SECRET (Cambridge 1987), and Hinich and Munger IDEOLOGY AND THE THEORY OF POLITICAL CHOICE (Michigan 1993).
Mark and I emphasized material interests in the case of Japan, not because we don't think ideology matters, but rather because Japan's particular electoral rules forced LDP politicians to compete on the basis of personal votes rather than on an ideologically-based party platform. The new electoral rules may well give ideology more play in the future, once the politicians and parties sort themselves out along ideologically congenial lines.