Thanks for the link. To me it seems strange to ask aircraft to fly runway heading. As I am sure you are aware drift is a function of true airspeed, and therefore aircraft on the same heading at departure will track differently if they fly different speeds. At Zurich, as at many International airports, the noise monitoring equipment lies along the SID. By flying a heading we invariably trigger a noise violation. Flying the runway track would more often than not prevent this happening.