Just because it's old, doesn't mean it's only about nostalgia.
Besides, I for one can't have this kind of nostalgia because in the '70, my fingers were a bit too short.
There is something extremely convenient to be able to use the same environment everywhere, with minimum prerequisites, because terminal emulation software is very common (probably as common as Web browsers).
I also find it more natural to deal with the system with a CLI when you spend your time editing source code or doing sysadmin stuff; it doesn't break the flow. Of course it's totally different if you're a graphic artist or a Web developer.
Sometimes CLI makes more sense, sometimes GUI makes more sense. But accusing people of being stuck in the past, that makes no sense.
UNIX shells can only seem powerful for those that never had the luxury of playing with Smalltalk, Lisp, Mesa/Cedar or Oberon environments.
Where you have a CLI and GUI experiences interact together to create a composable workflow experience.
Where I can do function composition on my REPL over data that I just selected with my mouse on a word processor, just to give a possible example.
Where public functions from dynamic modules are exposed on the REPL and can take part in any set of commands.
There is this primitive notion that a CLI needs to be the UNIX way, when a REPL as CLI is so much more powerful.
By "tab" you mean tab in your web browser; do you not? (I ask because there are non-web-based IPython thingies.)
edit: the comment by zorbo seems an interesting answer to my question, but I'm still not 100% convinced; also, I must still ask how can we be sure we're not victims of a text-mode "Stockholm Syndrome" in this regard?
So they look around and see only UNIX CLI.
It is just like mankind during the middle ages that never experienced how the Roman and Greek society were developed before the empire downfall.
Since I discovered UNIX, with Xenix in 1994 followed by many other variants, I always looked for ways to replicate such workflows in UNIX.
At the end of the day, Mac OS X and Windows communities are more welcoming to such ways of working.