* Plan 9's approach on terminal is entirely decoupled from the TTY idea. The terminal is basically a program that takes commands, has a shell run them, and pipes back the result, with none of the VT-whatever stuff. Even getting ncurses-based tools to run would require some effort.
* There's no X11
There are some graphical tools for Plan 9 (including more or less barebones web browsers), but there is just enough difference from Linux and BSD environments that people aren't quite willing to cope with it.
There is also an ncurses port and a vim port. I don't feel the need for either of those.
Edit: I share your point about the lack of need for either ncurses or vim (especially vim, hheheh). My first contact with Plan 9 was somewhat disappointing, mainly due to the fact that I approached it with the oh, Unix, I know this! frame of mind. I was very much a Linux fanboy back then (did I mention it was in highschool? And this is not the dumbest thing I did in highschool!). Only after I studied the source code a little, and learned rc more seriously, did I really begin to appreciate it.
I'd love to use, learn more about, and improve Plan9, but the lack of the above make it pretty painful.
This is why Hurd is probably far more likely to gain traction in the foreseeable future than Plan9.
In theory for vim and emacs you could work around that by using the graphical interface, much as say Acme does. I would estimate this to be at least as much work as porting from X11 to, say, Cocoa was, and possibly even worse. And this port would only get you a vim or an emacs that was materially identical to its Unix counterpart—no Acme style control FS and essentially no cooperation with the normal Plan 9 UI elements.
There's a vi for Plan 9 (even skipping the old joke about the MIPS interpreter...). I think it's vim, but I haven't paid much attention. David Hogan did a gcc port, and mostly nobody cared so it languished.