FWIW
The original paper for practical phase-correction in prisms (and other reflective optical devices) is
"Phase Compensation of Internal Reflection" by Paul Mauer, J. Opt. Soc. Am. 56, 1219 (1966).
in which Mauer, who was working for Eastman Kodak Company Research Laboratories, used a three layer coating to compensate the phase lag between incident llight and the reflected s- and p-polarized components from a corner cube reflector.
The original need for phase correction in roof prisms was noted in the early 1940s by a Dutch physicist (I think his name was Gill but I can't find the reference.)
Of course I don't have a copy of it but at least I could look up the paper at the UW.
You can see the abstract here (and buy a copy of the paper too!)
http://www.opticsinfobase.org/abstract.cfm?id=53137
Abstract: Symmetrical three-layer thin-film combinations are described which eliminate the difference in phase shift on reflection, of the S and P components of light incident beyond the critical angle. These three-layer combinations have low Herpin equivalent indices, but high enough material indices so that the critical angle is not exceeded until the final interface. Phase compensation is achieved at greater angles of incidence than those which can be compensated by single-layer films.
If you are not familiar with terms like s-polarizaed and p-polarized light this might help
http://en.wikipedia.org/wiki/Brewster%27s_angle
and for more detail
http://en.wikipedia.org/wiki/Fresnel_equations
Just trying to understand how the optics actually work!
Even from these rather simplified presentations it becomes clear that since there are an infinite number of variations in the refractive index of any medium (ie. glass) depending on the frequency of the light reflecting or refracting with it interactively, then all phase compensation coatings used in roof prisms are only rough approximations. Even if the number of approximations is increased to 60 or 100 or 1000 approximations across the frequency bandpass of light passing through the objective lens of an optical device, the phase corrections for the s and p light polarization problem is at best an approximation and would have to create more visual distortion that a porro prism system using surfaces exactly perpendicular to the lightpath direction.
Since all other factors are equal with porro prisms and roof prisms (ie. the cone shaped nature of the light beam accumulated and bent to reach the prisms, coatings for anti-reflection, fineness of polishing, quality of glass, eyepiece design etc.) ANY porro prism binocular made with the same materials and care as a similar roof prism binocular has to have better optical performance, because of zero phase distortion vs some phase distortion in any roofer made. Or am I misunderstanding Brewster and Fresnel?
There are places like Russia where the stampede to make and sell roof prism binoculars is much reduced because sophisticated purchasers can see that AT ANY Price, the porro prism model of an 8x42 for example, will outperform the roof prism version. It wasn't that difficult for Nikon to make their SE series (or Fujinon with the FMT series) as the easy choice for "Best visually" at each magnification level. If Pentax decided to make an ED version of the 7x50 DCF II WP they would likely be in this upper stratosphere optically as well, and they would be making a center focus, waterproof binocular with aspherical eyepieces that would likely be better than every 7x50 roof prism binocular in any comparable way.
I'm not sure why Zeiss doesn't make a waterproof internal focus version of the 7x50 Marine (anything Pentax can make I'm sure Zeiss can make), or why Swaro doesn't update their Habicht line, including models with ED or flourite lenses and high end coatings. Leica is committed to roofers at all costs, so that explains that and Minox doesn't want their expensive bins (now all roofers) with aspherical lenses to be compared to Nikon, Olympus or Pentax porros with aspherical lenses should Minox enter the porro market with a serious high end product. But until some company comes up with an infinite number of phase correction coatings for their roofer, it won't be as good as the porro they could have made with the same eyepieces and objectives.