Typos

I was recently reading a book in which there were several spelling mistakes.  How does this happen?  Editors are paid good money to catch various errors that, for one reason or another, the author had missed.  Admittedly, I make errors, too, but when you're paid to catch them, there's no reason for them to be in published works.  This book was good - not excellent, but good.  The thing that knocked it down a notch was the fact that there were SO MANY errors; there were at least 8.  I'm reading another book by the same author right now, and am barely a quarter of the way through it.  Already, I've caught a few errors (spelling, punctuation, grammatical).  If I can catch them, why can the editors not?  I find it very distracting, and takes away from my enjoyment of the story.  If I didn't like the characters and stories in this series so much, I would likely stop reading the books... but alas, they're vampires, werewolves, and other creatures that go bump in the night, so I am unable to shelve them :)