apenwarr muses on the value of professional copy- editing(sic), and writes:
After hanging out on the Internet for a while, you almost stop realizing how low-quality the content is. I'm generalizing here, but I include this very journal, and in fact, this very article, in my generalization. I think I'm a pretty decent writer, but there's no doubt in my mind: a professional editor can help you say the same thing, only better. ... The end result is odd: reduced publishing costs should leave more money for editing and fact checking. Instead, people think those costs should drop at the same speed, which is unreasonable unless you cut quality.and ends by asking of would-be readers: Would you pay more for quality, edited work? Really?
I think that this question is posed to the wrong class of people. When I buy a book, I will consider my money ill-spent if the writing is poor, and am quite likely not to read much of it. So there, yes, I would certainly pay more for an adequately edited book than for an inadequately edited book. Lots of other readers seem to think so, which is why we are not seeing quite the same economic pressure on book copy-editors than on newspaper copy-editors [1].
But for most classes of writing, it is not principally the reader who loses out from poor-quality editing, but the author. If readers of a weblog find it hard going, they will unsubscribe. The reader will not think twice about it; the author will be asking themself: why doesn't all that hard, content-creating work attract readers? If you want to attract more readers, better writing quality is important, and indeed the copy-editing mailing lists do receive reports from editors who have weblog-editing gigs, likely because edited weblogs attract more organic links, and so more revenue-generating traffic.
And for your book? Lousy editing attracts lousy reviews, which hurts sales, which hurts the author's reputation and the publishing house's sales (relatively few authors are motivated principally by royalties). Just where the most profitable mean is that avoids both overly-injured sales and unaffordable editing costs, the publishing industry has yet to figure out.
[1]: It says a lot when John McIntyre, former president of the American Copy Editor's Society, loses his job at the Baltimore Sun.