Last time I tried ansi-term and friends (not that long ago), it was very slow and struggled rendering my fairly vanilla (by some people's standards) shell prompt. Neovim's terminal emulation, by contrast, is a very great deal faster and can run Neovim inside itself with no discernible issues.
That's not actually a feature that was listed (because it's a pretty useless feature - I don't know anyone who actually uses ansi-term rather than screen/tmux, M-x shell or M-x eshell, and likewise it's not going to be useful for neovim to embed a terminal, the useful part is integration.)
