US sends military aid to SA as a mean of protecting their interests in the region. SA is not exactly a friend with Iran and the US makes sure their pumps don't change ownership.

nitpick. "SA" is usually the initialism for South Africa (RSA). For Saudi Arabia it's KSA, Kingdom of Saudi Arabia.

And the UK, whose arms sales to KSA are not exactly negligible.

http://en.wikipedia.org/wiki/Al-Yamamah_arms_deal

Arms deals and aid are different. However, you're right, and Alyamamah isn't the only one. The huge sums of money and fraud involved in all the arms deals between the Gulf Nations and the West is embarrassing to to both ends to say the least.