1/2 speed cutting not usually so good?

Any mastering engineer or other person in the know care to comment on Bob Ludwig's letter in the March issue of The Absolute Sound where he indicates that 1/2 speed cutting is a trade-off. He says that a cutter head flat to 20Hz is only flat to 40Hz at half speed. In combination with the RIAA cutting curve, Ludwig says that an additional equalization circuit is needed for 1/2 speed cutting that introduces extra ringing and distortion. He concludes: "For some music, half-speed cutting is an advantage, for the majority, probably not."
Perhaps I misunderstand the process. But if I have it right, some other folks including those at Mobile Fidelity may want to provide a different viewpoint.