You need them because the examples are intentionally simplified. Even a data structure as simple as a dictionary has a useful variety of iterators: over keys, over values, and in some languages, over (key,value) tuples. Explicit iterators are really only noise for the "natural" iterator, i.e. in order iteration over an array.

I agree that having it hidden by a language feature is nice, but somewhere there is an iterator -- the class that supports that iteration must at least specify how it's accomplished. I would prefer if there were an easy way to integrate with the range keyword in Go.

EDIT: Adding to reply to some added comments. The close() one in particular really threw me. It makes sense in terms of how channels work, but is really unfortunate. When I first saw the channel-based approach, I thought it was a neat solution. But then I found all the problems with it (including the best example I could find of it online missing that close(), which is why I pointed it out!).

I think Go is close to getting it right if they would do what I mention at the end of the article: provide a way to hook into the range keyword.