Israel wants the Egyptian Army happy, thus whenever the US threatens to cut support to the Egyptian Army, Israel lobbies Washington to keep them. The Egyptian Army then rips off that aid to their own pockets and every one is happy.
Israel and the US knows that if Saudi Arabia goes into Civil War. Such a Civil War is a good possibility, increasing every year, but so far the sons of King Saud I, died 1952, have managed to prevent such a Civil War, the big question is as that generation dies out, and it is dying out, what will their sons do? In most such situations, it is the third generation that tears a country apart as they fight over control (their fathers, being all brothers, grew up together and thus reluctant to kill each other and thus tends to stop short of any bloodshed, that is NOT true of the third generation, who are slowly moving into positions of power in the Kingdom of Saudi Arabia).
In such a Civil War, the worse thing Israel or the US can do is send in their own troops. The two holy cities of Islam is in Saudi Arabia and any US or Israeli troops that goes near either city faces the possibility of a full scale holy war. On the other hand, US and Israeli support for an EGYPTIAN ARMY INTERVENTION avoids that whole issue. Given the area of Egypt, you have to have a decent size army to take it over, the only countries with the population to support a decent size army are Turkey, Iraq, Iran and Egypt. Turkey, while Islamic, has a bad reputation from the time of the Ottoman Empire (and really want nothing to do with the rest of the Middle East if it can help it). Iran was possible, when the Shah ran Iran, but since 1979 Iran is NOT an acceptable intervener. Iraq, under Saddam was NOT an acceptable intervener and given that Iraq is slowly becoming a close ally of Iran, it is also not an option for the US or Israel.
Thus, that leaves Egypt, a role it has accepted since the late 1970s when it agreed to a separate peace with Israel, in exchange for massive US support for its own military. This is the main reason we are buddy buddy with the Egyptian Military, it is our main option in case Saudi Arabia goes into Civil War.
Egypt provided the Second largest ARAB army in the First US Gulf War in 1991. Egypt supplied 20,000 men, Saudi Arabia was #1, at 60,000 men, but it sat out the second Gulf war given the level of internal opposition to that war (The US supplied over 600,000 men, yes 2/3rds of the "Coalition" in the first Iraq War were US troops).
http://en.wikipedia.org/wiki/Coalition_of_the_Gulf_War
While Egypt did not participate in either Gulf War, neither war involved any actual threat to Mecca (Mecca is on the other side of Saudi Arabia). The problem is Mecca, and the possible need for some sort of "Islamic" army to take it if Saudi Arabia breaks down. The Egyptian Army can do that, if supported by the US and Israel.
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