First, typos exist. It is a very rare book with no glitches. Some misspellings, incorrect word choices, etc. have been in the text since the original manuscript and have defied detection by the author in numerous revision passes, and by other editors, and beta-readers in their readings. The human mind is wonderfully adaptable in making sense of incorrect and fragmented raw material. Computerized spelling and grammar checkers have their own defects, so much so that they have become a source of jokes on their own. The conversion from manuscript to final layout also has the potential to increase errors. And now, the conversion to ebook versions just adds another layer of glitch.
So when the text goes out into the wide world of readers, typos will be found. As Maureen said, "No one is bulletproof". And as an author at the mercy of a traditional publisher, she said, "The thing is, I can't actually fix them. All books have mistakes, sadly. All authors are sad for this. Really. We are."
Here's a difference for me. I'm one of these crazy self-publishing guys. I control the whole chain from manuscript to pages on the bookstore shelf. If there's a mistake, it's my fault. It also means I have the power to fix it.
Here's one example: I was in a bookstore in Michigan while traveling, attempting to get Lighter Than Air accepted on consignment. The lady in charge picked up the book, glanced at the back cover text and instantly said, "'Peninsula' is misspelled." She took the books anyway, but devastated, I didn't even leave the parking lot until I had googled and searched and determined that in spite of my firm conviction to the contrary, it wasn't spelled with 'nn'. Since this is a POD book, I was able to revisit my cover artwork, correct the spelling, upload the correction to Lightning Source and pay the $40 fee for the correction. Luckily, it was spelled correctly in the body text, or that would have been another $40 to correct it there.
That's the basics. I can correct even the simplest of errors. The question then becomes whether it's worth doing. Not only do I have to correct the master files used to print the trade paperback versions, but I then have to correct and upload the master versions of all the various ebook versions. It's time consuming. If I had an assistant, I'd make it a priority.
In reality, I have collected all the emails I get with typo information in a special mailbox. If it's just a simple, commonly misused word, I'll defer the correction until later. Then, I'll collect all that information and correct everything in one pass. If it's a more serious issue, like a big blatant misspelling on the back cover, I'll clench my teeth and do it as soon as I discover it, plus anything that's been waiting. If I had waited just a little longer to fix the 'peninsula' problem, I could have combined that fix with the addition of the "Winner of the Golden Duck Award" addition that cost me another $40 fee to process.
So, I welcome any discovered typos, and indeed any other kinds of errors. I may not fix them instantly, but they won't be ignored.