For me, author is someone who writes a book. It would seem weird to call a poet an author, at least to me. Or a journalist, unless they have written a book. Yet all three of them are writers.
Plus, there's people I'd consider writers who aren't published, and, therefore, not authors. Though it could just be a quirk in my idiolect.
That's interesting. I don't make that distinction, since I refer to poets as authors all the time. I do sometimes make a distinction between author and writer, but it is usually in a history class, when I am distinguishing the person who conceived the words from the scribe who actually wrote them down.
Well, I am not terribly well-versed on how the roles might have been designated in Old or Middle English, but the distinction between auctor and scriptor (I don't know whether the Irish are borrowings or just cognates) lost most of its usefulness with printing. When I have students think about the production and transmission of ancient and medieval texts, I make this distinction. Of course, the distinction we are drawing here is no longer between the creator of a text (or anything else in the case of the Latin word) and the scribe of it. English is, of course, spoken quite widely, so I can only speak anecdotally about my own experience, but for instance, my daughter attends an arts high school in Chicago and the one of the conservatories within the school is that of the writers, including poets, playwrites, fiction writers, and even non-fiction writers. That said, when I use the term author, I do think it stresses the relationship of the writer with the text, usually a particular text. Indeed, I don't think I would refer to a person as an author in general, but rather only in relation to a particular text.
English is so odd. I only ever call poets "poets," even when they write poetry. I use "author" in reference to someone who writes, novels, etc. Then again, someone can "author an idea," which doesn't involve writing at all!
After looking up the etymologies, it appears that - as usual - modern English is using two words that mean nearly the same thing, but one is borrowed from Latin and the other is descended from Old English. "Author" does seem to allow more of a creative attribute to the act of writing, i.e. being the presenter of something new, whereas "Writer" is just someone who can write.