Just to add a recent data point:
DONE4 ex-CMB commenced December 06:
Base fare: LKR 592,200
Add-ons: LKR 90,000
Courier: LKR 2,200
Total: LKR 684,400
Extras just over 15% of base fare (just over 13% of total).
Route: CMB-xHKG-LHR -xDXB-xLHR-xORD-DCA -Surface IAD-xDFW-xSYD-CBR -xMEL-CBR -xSYD-xHKG-CMB
Dave Noble is correct (you have no idea how sick I am of saying that

), ticketing with AA in CMB can easily save around US$400. It wasn't feasible for me on this trip (it would need an overnight in CMB), but I will do it next time.