Recently rumours were around that some USAF intelligence people had a nightmarish delusion that Ma Jing-yeoh will give a bunch of the newest AMRAAM´s to Hu Jintao as a wedding gift in 2008.
(just kidding!)
The US maintains a very deliberate weapons export policy for decades now (learning from the 1979 desaster in Iran): Do not sell the most advanced offensive long range weapons (ASM, AAM, AShM etc.) in any substantial numbers if the recipient does not classify as a
very stable first class iron clad ally. (i.e. UK, Canada, Australia,Israel plus some euro NATO-Allies (Germany,Italy,Poland) and Japan (South Korea may lose this position soon)).
All the other so called friends and allies (Saudi Arabia, UAE, Kuwait, Egypt) get only degraded crap for which they have to pay a hefty price. The saudi F-15-S is simply a completely impotent ´Strike Eagle´without effective missiles and the israelis keep on laughing about the egyptians lunacy of buying more than 200 old-block F-16 without enough short range AAM´s for self defense. Pakistan did not even get her
already paid F-16 since the paks were not obedient enough regarding their nuke program.
So if you keep the tabs together the reason for not selling substantial numbers of AMRAAM´s to Taiwan is quite clear:
Washington does not regard Taiwan as a completely reliable and subservient ally anymore. DoD analysts conclude that after becoming rapidly economically dependent on the mainland the future course of Taiwan will be in the direction of reintegration or at least accomodation with Beijing. That interpretation of facts may be wrong but nevertheless
this is arguably the root cause for being so hesitant in arms deliveries from US to Taiwan for some years now.