GUIs - not just for your grandma any more!
I've been working in Unix for over 20 years. I speak shell and Emacs as my native language ;-) I use the command line commands for exactly the same reason I use GUI apps, Finder plug-ins, or any other tool: because it's the tool I want at the interface I'm using at the moment I find I need it.
There are some things that can't reasonably be done with a GUI; there are some that can't be done well at a command line. There are a few more that can be done either way, but are inherently better one way or the other. There are a few more that could maybe be done better "the other way," but no one's got around to writing that yet. Anyone who calls themselves "a developer" should be plenty smart enough to use the best, or anyway handiest, tool for the job at any given moment. If you're not solid in GUI, command-line, regular expressions, scripting, and keyboard macros ... are you sure you're a developer?
And *don't* get me started on "I only know language X"!