Furthermore, nothing is said at all about the influence of cosmological electromagnetic fields, which are simply assumed not to be important.

This one has always got me. I mean, even on an intuitive level, electromagnetic forces are /d², just like gravitational forces - stars (hell, galaxies) are huge spinning masses of plasma - how can you ignore possible effects? Not to mention that we know essentially NOTHING about even interstellar space, more or less intergalactic - we know so little about it, scientists just put stuff there (like dark matter) when it makes for convenient hypothesis...