Both a violin and a guitar use some of the same acoustics principles and techniques, but guitar players can't just pick up a violin and start playing it (or vice versa). The guitar experience may give an "edge", but in the end it's a different skill.
And it's the same with Vi and Vi-like bindings in bash. People who come to this site are experts (or at least proficient) with Vi, and not necessarily with bash, Vimperator, or anything else. It's simply a different skill and interest.
From the comments:
A shell is usually required to access vim, and it's VI mode is universal given the limited number of shells in use. It is also widely used and usable by everyone. A Random Program or Plugin for Firefox giving vim-like functionality is far more exclusive. This is the qualitative difference.
I'm not sure if this is a very good argument. A keyboard, monitor, CPU, power supply, Operating System, the C standard library, and much more is required to "access Vim"; none of which is even remotely on-topic on this site ;-)
Part of the motivation is that I feared that this SE would be too limited in scope, and would not have enough questions.
Beta sites don't get closed for "not enough questions". There are some sites that have been in existence for much longer with a lot fewer questions. As long as we make sure the quality stays reasonable we should be fine.