Ugh...I just finished another book that had at least one misspelled word on nearly every page. Word usage common to Civil War contexts is another endless problem. Innumerable writers can't seem to appreciate the difference between 'ordnance' and 'ordinance' and if I have to read about one more 'eminent' attack I am going to scream.
Since I know nothing of the hardware and software involved with modern publishing, I can only guess at the most common source of the problem--man or technology. Anything's possible these days with the increasing lack of editorial oversight, but it is still hard to imagine an author submitting a manuscript containing hundreds of spelling errors...or perhaps it isn't! Just in terms of spelling, if you hand over a clean manuscript to POD establishment Authorhouse and send the same to Chapel Hill will a clean book come out of both? Or is the difference the no staff at Authorhouse vs. trained professionals at UNC? Or are outcomes based on a mix of both on a case to case basis, immune to generalizations? I would love to be educated about the quality control steps taken by great publishers like University of North Carolina Press compared with the omissions of Press X (fill in your favorite consistently bad traditional publisher).