Not necessarily, imagine for example an embedded OS with only dash or busybox based on Debian.

Also, even with bash installed, bash doesn't always behave like sh does.

A common example is echo:

With /bin/sh on an OpenBSD:

>>>

kakwa@openbsd ~ sh -c 'echo "print\n"'

print

<new line>

>>>

With /bin/dash (aka /bin/sh on Debian)

>>>

kakwa@debian dash -c 'echo "print\n"'

print

<new line>

>>>

This is consistent so far.

But, now, with /bin/bash

>>>

kakwa@debian ~ » bash -c 'echo "print\n"'

print\n

>>>

That's why I tend to use printf more than echo in my shell scripts.

Also, I'm not a big fan of what RHEL/CentOS/Fedora does symlinking /bin/sh and /bin/bash. It blurs the line between bash and sh, which results a lot of scripts with a /bin/sh shebang containing bashism.