Google "should be" able to tell the difference between articles written by different authors. Certainly there are varieties of linguistic analysis that can do this - they've been around for years and years. I'm not saying Google does this right now - just that they could use it as a tool to protect against "author spamming" attempts.
That said, I do know of one case where a group of well established authors were writing for a website and their content was being outranked by scrapers. The authors all agreed to setting up Google+ authorship for their articles and within just a few weeks, the scrapers fell away. YMMV, of course, and even though the timing was very suggestive, the site did make other changes at the same time.
I do think, with the right care and feeding, Google can make something good of author mark-up. I can even see that links from an article written by a well authenticated author might get some kind of boost in their effect some day.