Many of these are very usable for their target audience:

Vim: adds such user-friendly features as syntax highlighting and WIMP while keeping an interface (vi) that is already well known to it's users, thus preventing them from having to learn a new set of commands from scratch

Emacs: Clearly the most programmable text-editor currently used. The ease of usability for extending it is the reason it is adopted.

mutt: synthesized interface from several already existing mail clients, most notably pine and elm

Apache: If you consider the user to be web developers, it (NCSA HTTPd which is what Apache grew out of) introduced CGI, which was a huge usability step for making dynamic web-pages.

Linux: Not sure. It's essentially a clone of SVR4; probably just the fact that among it's always had the best driver-support on commodity hardware is the win here.

Postfix: It's more usable than sendmail; not really a glowing review though.

X: Yeah, I can't think of a single good thing to say about X. I've heard that Motif was the "killer app" for it that kept it around, but I wasn't there so not sure.

All those you mentioned are highly configurable and accessible through the command line interface. For the target audience, they are highly usable. 'Traditional' (if we speak of the same thing) does not care if your users are general users or engineers.