Chuck is quite right about this degenerating into b.s. - I didn't intend that. This kind of scattering is mostly caused by the molecules in the atmosphere, which are much smaller than the wavelength of light. So the exact kind of atmosphere isn't really the issue, although the diffuse skylight falling on other planets might be different due to other processes, e.g. absorption. What I object to is that someone has branded the fourth power law "empirical". While it was indeed empirical when first observed, it can be derived either from classical electromagnetic dispersion theory or by quantum light scattering theory. While it may be popular in social science circles to put quotes around "law", etc. at least some of the theories in physical sciences have experimentally verifiable consequences.
BTW, Rayleigh scattering is also responsible for sunsets being red: here we are looking at direct rays of light which have had the blue end of the spectrum scattered into random directions. Because these rays go through a thick layer of atmosphere this becomes apparent.
Cheers, Joe Moryl