I dunno if it's actually vim or some variation on it, but it is the default on, for example, Arch Linux, although I believe most other distros dropped me into it as well (e.g. git commit / rebase -i).

If there is such a thing as user hostile in the world of CLI tools, then dropping the user unannounced into vi with some open buffer most definitely counts as user hostile.

Don't know about $EDITOR, but if you issue a git commit in Windows, and forget to specify -m, then you end up in vim.

In Jessie, visudo lands you in nano, unless you explicitly set the $EDITOR.

What are your thoughts on $VISUAL?