Different perspectives; Emacs has a built-in shell, which is closely integrated with most of the editor's functionality -- for example, Tramp, which transparently supports almost every remote access protocol in existence; if I want to copy a directory tree from host A to host B, in bash I might
mkdir ~/tmp/foo
scp -r user@host-a:/foo/bar/* ~/tmp/foo
scp -r ~/tmp/foo/* user@host-b:/foo/bar
rm -rf ~/tmp/foo
or
ssh user@host-a 'cd /foo/bar; tar -cf - .' | ssh user@host-b 'cd /foo/bar; tar -xvf -'
while in the Emacs shell I just
cp -r /user@host-a:/foo/bar/* /user@host-b/foo/bar
and if I want to inspect the result, in bash I
ssh user@host-b
ls -R /foo/bar
while in eshell I simply
ls -R /user@host-b/foo/bar
and all the key management happens automatically, via ~/.ssh/config and ssh-agent, just as it does when I invoke OpenSSH binaries by hand.
Oh, and lest I forget, if I want to edit a remote file in Vim, I have to either ssh to that host and invoke vim there, or scp the file here and invoke local vim on it, or deal with sshfs or something -- the latter of which might seem like a perfect solution, until you consider that I use all of Linux, OS X, and Windows machines extensively in my daily life, and not all of them do sshfs well or at all. By comparison, eshell's
find-file /user@host/foo/bar/file
is exceedingly simple, and works equally well on whatever machine I happen to be using at the moment. I don't have to worry about marshaling temp files or configurations or, indeed, anything at all; Emacs does all of that for me, quietly, in the background, so that I can spend all my time and mental effort on the changes I actually want to make, instead of doing a bunch of annoying sysadmin work just so that I can make them at all.
There's value in having lots of loosely coupled tools, but it's not the only paradigm worth considering. There's also value in a single, unified interface to an enormous range of tightly integrated functionality; indeed, I've found the result to be something of a combinatorial explosion of productivity.