From the standpoint of the American Jews' choice between Republicans and Democrats, what you say is largely true. There is too little difference in the day-to-day operations of government, no matter which party has the majority, to give anyone, Jew or otherwise, much of a reason to favor one over the other.

However, Scott's question is larger than American politics.

The philosophical underpinning of Judaism teaches that we humans have an obligation to assist God in the completion of creation -- it's why we were made. The concept is called tikkun olam, literally "fixing the world".

Conservatism seeks to keep things as they are. Liberalism seeks change, in order to improve. That's why most Jews are liberals, even if they vote for Republican politicians.

As to Scott's simplistic invocation of US policy vis a vis Israel as an indicator of "being Liberal":

There is an unfortunate tendency among many people here to define loyalty to a country strictly in terms of loyalty to its leaders. Inasmuch as any Diaspora Jew might have a loyalty to Eretz Yisroel as the Holy Land, it comes after his/her loyalty to the country of which he/she is a citizen, and has no bearing on Israeli politics.

In other words -- it is not only possible, but extremely likely, for any given Jew, whether they live in Israel or not, to support Israel by opposing the actions of the Israeli government.