The reason the airport link works in places like HKG and won't work in BKK is that the cost difference between taking a taxi vs the train is a major factor. With 2 pax, its cheaper to take a taxi to BKK. Plus, the time to get to the in-town station, purch train tix, and then wait for train, and then ride 3 sets of slow moving travelators up to the Dep Level. Crazy!