Post-apocalyptic broad-gauge rail

I re-read Sean McMullen's Souls in the Great Machine after my UK trip. The second half of the book does make a big deal of the (Australican) Great Western Paraline Authority, and its worship of Isambard Kingdom Brunel, and its engineers' fanaticism over seven-foot-gauge rail vs. standard gauge...some two thousand years after "Britancal heretics" tore up the last broad-gauge rail on the real Great Western in AD 1892. I'm not really clear if McMullen is mocking present-day GWR fanatics in a way that only hard-core rail geeks would get, or if it's supposed to be making a statement about post-Greatwinter Australican society, or what. It's very vaguely plot-relevant at one point (item relevant to very high level plot is stuck at a particular place because the rail gauge changes), and it turns out that the Brunel worshippers do know things that everyone else has worked very hard to find out, but it just seems somewhat gratuitous to me.

I'm still trying to work out how the Wanderers destroy anything moving larger than twenty-nine and a half feet in Colandoro in The Miocene Arrow but they let the Australican galley trains run without issue.