To put it simply, the only time you'll see Singapore AH-64Ds in action against jet aircraft is when our country is already on the verge of being completely taken over. I don't think any of our generals really think 8 Apaches will do nuts against just about any real threat in Asia, not when Malaysia has MiG-29s and is thinking of getting SU-30MKMs. Not when our fleet consists second hand 70s-era planes like the F-5, F-16, and even the F-15. The purchases of all these American aircraft is very much more of a 'you rub my back and I'll rub yours' sort of deal, in my opinion. We pump some money into the American aeronautical industry so we can count on them if we're attacked.
EDIT: Did I mention Malaysia's F-18D Hornet? LOL