  We consider the amplification of cosmological magnetic fields by
gravitational waves as it was recently presented in [gr-qc/0503006]. That study
confined to infinitely conductive environments, arguing that on spatially flat
Friedmann backgrounds the gravito-magnetic interaction proceeds always as if
the universe were a perfect conductor. We explain why this claim is not correct
and then re-examine the Maxwell-Weyl coupling at the limit of ideal
magnetohydrodynamics. We find that the scales of the main results of
[gr-qc/0503006] were not properly assessed and that the incorrect scale
assessment has compromised both the physical and the numerical results of the
paper. This comment aims to clarify these issues on the one hand, while on the
other it takes a closer look at the gauge-invariance and the nonlinearity of
[gr-qc/0503006].
