PN - I suspect that the Germans likely did reconise the importance of the rail network but at that time didn't have the resources to take it out to any significant degree, their efforts being focussed on the main cities, airfields, and industrial facilities.
I can't comment on the Russian railway system but could it also have been a factor that the UK rail system (pre Beeching) would allow rail traffic to divert around any areas that were taken out? (perhaps analogous to how the internet routes info around busy nodes).