It is true that the Israeli economy has taken off in the last decade, mostly because of its advanced high tech sector. This was not always true and for decades Israel's economy was under stress as a new nation integrating people from all over the world while having to defend itself from hostile neighbors. In those days, U.S. economic assistance was critical for Israel.
Today, Israel no longer receives U.S. economic assistance. This, indeed, is recognition of the advances in the Israeli economy. Military assistance is another matter and reflects several particular factors that apply to Israel, its situations in the Middle East, and its relationship with the United States.
From its independence in 1948, Israel has been in a unique circumstance as a state whose neighbors denied Israel's right to exist and who took steps, military and otherwise, to try to end its existence. Unfortunately, that situation has not completely changed. Countries like Iran and groups like Hamas and Hezbollah are openly committed to Israel's destruction.
As a result, there is a tremendous burden on Israel to maintain a military that will deter its oil-rich neighbors from achieving their goal. U.S. aid to Israel recognizes that unique situation that our ally has been in and has worked with Israel to ensure it maintains a strategic military edge to deter its enemies.