"If either of you are Professional Pilots.... get back in the books."
Nigel,
I don't think I was slagging any-one off and suggesting you get off your high horse is entirely reasonable when you wade into a technical request with the above statement.
Perhaps, if you stop to think at all, you may realize that the (not very) technical explanations I have given, together with examples of other instances of inaccuracy ('not quick enough to keep up with turns') serve to help solve the 'quirk' the poster queried.
And my reference to asking of the relevance of the WV vector during TO is supported by mcdhu's note on the A320 ('W/v comes onto the ND at 100KIAS')
Having appointed yourself the cleverest amongst us, please give the poster a full explanation of the wind velocity indication on the B-738. Otherwize, your opinion is only as relevant as everyone else's.