Rolling off before the microphone amplifier means that bass frequencies can't saturate the amplifier as easily.
I get your point, but I thought we had plenty of dynamic range available these days. Judging from the text, they seem to use it rather like an equaliser anyway.
Regardless of your dynamic range, in order to have maximum S/N you have to run as hot as feasible. So there's no point capturing and amplifying any signal you already know you don't want.
Fixing things closer to the source is usually best.
Both the mics in the article have output transformers. It's really easy to saturate a transformer with excess low-frequency sound, so that's part of the reason to have a high-pass filter earlier in the signal path.
You're right, though sometimes simplicity beats flexibility. It's a lot easier to set it as a standard right at the beginning of the signal chain and frees all the engineers down the line from having to make decisions about it, and ensures consistency in the process.
There is bass rolloff in the mic even when set flat. This is the proximity filter designed to correct for the way the mic responds when it is close to a source.