Nigel pointed me to this thread and wondered if I'd like to comment. I found it very interesting!
Being completely objective about it all, I didn't see Rob's comments as spiteful. I personally feel that if an author takes affront at polite and constructive criticism, then that author should quit writing at once and get out of the public eye. I'm sure Julie isn't offended, though -- right, Julie? I'd be disappointed if you were.
Readers occasionally point out typos in my books, and my reaction is, "WHAT? Holy cow, thanks so much for letting me know, I'll correct it right away." I can't fathom why someone would be unsure about mentioning it. It annoys me that a reader would keep that information to themselves. I want my books to be as clean as possible, even if that means re-publishing. I publish on Amazon, Nook, Kobo, and Apple, and also a print edition on CreateSpace... so yeah, that's a lot of re-publishing. But it's worth it. I've had quite a few reviewers over the years say they appreciate "error-free" text in this typo-riddled publishing world we live in now.
Julie, you asked why on earth would someone go back and keep proofreading? Well, I wouldn't go so far to say that I'd keep on and on re-reading my books, because yes, that would drive me crazy, always finding new things to fix. But I'd certainly want to know about typos. My own way of doing things is to re-read the book several times BEFORE publishing, and have beta readers read it as well, and fix everything I can before I hit the publish button. Then, as I said, correct any new typos readers might point out. But I won't re-read it myself; I'm done and have moved on.
One thing I'm certain about is that you can permanently screw up your writing career if you don't make your book as clean as possible. I've seen reviews for books stating that it "would have been a good story if it had been edited or proofread properly" and those readers actually giving up and giving it a low rating. That cannot be undone. When a book has 100 ratings, and the first 25 are 1-star because it was poorly edited, but the book has since been edited... well, it's too little too late.
Oh, and vanity vs. self-published... I would never, ever pay hundreds of dollars for a "press company" to publish my book. I won't even pay a cent. I'll do it all myself for free, thankyouverymuch! And being self-published can be the smart way to go these days. Typically, a traditionally published author might feel they're being fully marketed and promoted... but I'll bet most have to do all the work themselves, only for a much smaller royalty than self-pubbed authors. Only the big names, or the potential big names, are promoted properly. The rest fend for themselves. Read about it. You'll find that most traditional publishers take on maybe ten books a year and will pour all their attention into the two top "favorites / best bets" only.
That said, if a traditional publisher came along and offered me a 6-figure number for one of my books, then I'd pay attention.