To the Bush's administration Israel is still collateral for getting to Iran's oil. Its cheaper to fund billions of dollars in weapons to Israel and have Israel pay in credibility, effort, lives, suffering for an ultimate US goal (It helps the US to have Israel in conflict with its neighbours). This way it saves having to sacrifice US lives, and it goes down much nicer with the voters. Why do you think Rice is constantly visiting Israel.
Monitor: Clashes near Damascus despite truce there, five killed in Aleppo (Reuters)
from the article: Report: Cheney may have mulled pushing Israel to hit Iran