When you're a small-town newspaper, it's easy to let errors slip through, especially if you don't have a lot of eyes looking at your stuff and the editor is also a writer. You can read and re-read and re-re-read your own stuff and miss stuff that becomes readily apparent as soon as you see it in print. At the paper I edited for eight years, we had an eagle-eyed proofreader (the publisher's father) who could catch even the tiniest of errors. When he died, I'm not ashamed to say the quality of the printed product went down because stuff would slip through that he would otherwise have caught (such as the time I misspelled the proper name "Burgher" as "Burger" in the jump head of an obituary.)
I've been alarmed, though, at the number of errors I'm spotting in big news outlets. Not only punctuation, spelling, and capitalization, but basic grammar and other errors such as extraneous words that don't belong.