When most people think of the job of being an editor, I think they imagine someone hunched over a desk, red pen in hand, marking up an endless stream of text, cleaning up split infinitives and dangling participles and the like. But the editorial role and the editorial discipline are two very different things. While there are definitely some people who specialize in this sort of work, there's usually much more to being an editor.
In the broadest sense, an editor's job is to help writers make their writing more effective. This involves grammar and punctuation and word choice, sure, but a huge part of any editor's job has to do with creating effective structures. An editor might be responsible for structures at many scales, from the encyclopedia down to the textbook down to the article down to the paragraph down to the sentence.
Like the editor, the information architect is concerned most fundamentally with creating information structures. But the discipline of information architecture views this responsibility in a very different light. In the world of information architecture, all structural challenges are currently viewed as variants of the same problem -- the problem of information retrieval.