Yesterday Sven Hartge responded to my query regarding rsync, quoted below.
However, my question was not a technical question asking why rsync was not automatically installed during a stock amd64 debian installation, but a more philosophical question as to why the debian administrators chose to make rsync optional, given the importance of backup data.
Thank you to Sven and to those who have read and considered my question.
Date: Sat, 4 Nov 2017 22:20:52 +0100
Subject: Re: rsync
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> I find it fascinating that the stock amd64 netinst 9.1.0 installation
> did not install rsync. Does anyone know why that was not automatically
> included? Yes, this was easily remedied, I just find it fascinating
> that it was no longer included.
rsync is "Priority: optional", meaning it is not automatically installed
unless a package depends on or recommends it.