Most of the features Vim is used for don't exist in vi. Vi doesn't have visual mode, syntax highlighting, multiple level undo etc.

Also, Vim is 20+ years old as well.

Edit: grammar

The irony of calling somebody out on a false statement with a false statement of your own...

Vim is more or less a superset of vi. Even still, there are some subtle behaviors in real vi that do not work the same in Vim, even in Vim's "compatible" mode.

Of all the vi-like editors, Nvi is much closer to real vi than Vim is.

What? That's not true at all, though I don't know about the "more advanced" functions, since I quit vi and start using vim as soon as I can - because even things like insert mode completely differ.

I can see how technically, you can consider them the same. But anyone who's used to vim will have quite a bad time in vi because of all the things that don't work.

"Most of vim is from vi" doesn't mean it is same. For Vi != Vim to be wrong (or Vi == Vim to be true) everything that Vim provides MUST work with vi as well - only then they are same/equal.