But I guess what you are saying is that under *nix, the standard
CRT input routines don't provided line editing facilities, unless the
program in question uses a readline(3) library or similar.
Essentially yes. stdin is just a file handle like any other,
which by itself is unfiltered / binary-clean. Any other behavior you
may observe (typically with interactive sessions) is the result of
other layers that sit in between stdin and the user/keyboard, most
prominently a tty and (optionally) some readline library.
When stdin is connected to a regular pipe for non-interactive
communication, those layers are not involved, unless things have
explicitly been programmed that way (as with tools like Expect or
similar) — this of course can be done, but usually isn't.