The Royal Malaysian Airforce bought the 18 Su-30 because of the sales package offered by Sukhoi, advanced weapons system (fitted for but not with R-77), TVC engines, custom-built modifications. In short, we have a say on how we want our fighters, not much but definitely much more than the US were willing to give us, as words got around that the US resrcited certain features in the F-18D that was bought earlier making them very limited in terms of offensive capabilities.Take also in consideration the Iraqi war in which the Malaysian Government bitterly opposes, it would seems bad that the Malaysian government would support the US arms industry by buying the the same F/A-18F that just months earlier been striking Iraqi targets so recklessly.
There are rumours however that the government would trade-in the old Hornets and buy the F/A 18F but this seems likely to be on very long term planning as the Malaysian defence buying cycle seems to come to an end. It is highly likely that US is not the no 1 defense provider for malaysia anymore as it seems that they are turning to EU and East European. (Russian missiles, Polish Tanks, German OPV, Turkish IFV, Brazilians MLRS).
However, it is interesting to watch to whom will the Malaysian Government turns to when it wants to purchase the last major item in its shopping list, the AEWC planes. Current speculations favours the Erieye.