I have trouble with this justification as well.
The formulae are not once presented in-game, at all. Thus, the only people to whom the exact details are given are forum-goers. It would surprise me if the divulgence of the exact values would really generate the support calls as asserted (unless the calculations themselves are bugged, but I’d argue that reporting bugged calculations is good for the game).
The other reasons given may be valid, but all in all I dislike the lack of transparency here. I have no skin in the game, as I don’t do GW, but if I did I’d be much more vocally opposed to the secrecy.