Try to say 200 at 20 over the HF sometimes and see how that goes down with the poor soul trying to hear what you're saying on the other end.
200 diagonal 20 is a direct reading out of the FMS (200/20) and at least what I was taught to use as it makes it clear that you are reading the wind at the end of a position report.
I guess the guys just continue to use that even on a clear and crisp VHF over Euroland.
Proxus