I was pointing out two separate things which occurred:
1. German train crews relentlessly checking and re-checking and re-re-re-checking train tickets after each major stop, rather than (as with every other country) checking once, noting the passenger's destination, and then not bothering them again. This was not an identification check, it was a ticket check. This is primarily an annoyance, but seemed part of a pattern of much stricter controls imposed by German crews and within Germany in general, as corroborated by...
2. At the first stop inside the German border, police -- that is, officers in uniforms which read POLIZEI -- boarding the train and carrying out a check of every passenger's identification. This was not a ticket check, it was an identification check.
At that border stop I was also asked, by an officer who did not speak sufficient English (and I speak no German, only English and French) and so had to show me printed cards and ask me to point to answers, the purpose of my visit to Germany and the duration of my stay in Germany. This was asked despite my already having legally entered and having remained continuously within the Schengen area (my passport, already displayed by that point, contained the entry stamp, ironically from an airport in Germany), and despite my already having entered Germany twice on that trip.
As a result I am extremely skeptical of the idea that Germany has an "open border" or "no border controls" for intra-Schengen travel. That border stop on a train, coming from another Schengen country into Germany, was actually more in-depth than the examination at my initial entry in Frankfurt airport.