I think UserMark is right. ITN shows class availability, but it does not show you the fare of that particular class or allow you to book in that class. (Ex. JFK-HKG. Booked in Y = $2500, B = $1900, Q = $1100) ITN tells you that B is available, but it doesn't tell me that the fare is $1900 nor can I book it online. Most websites lets you book the lowest fare (in this example, Q) or the full-coach fare.

EasySabre gives you the fare and let you book in any class that is valid.