That's precisely the parent's point. The Vim model (I'll exclude vi from the discussion since it lacks core aspects of Vim's composability like text objects, and almost no one should be using it) is about having a largely inflexible editing language built off of composability. The Emacs model is built around infinite extensibility instead. That's why implementing Emacs in Vim would be fundamentally at odds with the principle of Vim, but it's very possible to implement the Vim model in Emacs, and Evil does a nice job.
Well, there's vimacs (http://www.vim.org/scripts/script.php?script_id=300) which gives you the basic keybindings and modeless editing. I agree though that the vi modes for emacs give you more than the emacs mode for vi.
I started out in Emacs, used it and customized it for years. Then I decided to see what I was missing in Vim, so I switched entirely for two years. I became very comfortable with that world.
Then I spent about a year in the strange netherworld of viper-mode and vimacs, switching around more or less at random.
Eventually, I landed back in plain emacs for most things and have been there for the last ten years. I have nothing against vim and still use it from time to time, particularly when I'm working on a remote server. I just realized that for me, emacs was at least as capable on every front and seemed to suit my way of working better.
