Here's a little tradecraft for you. Copyediting and Proofreading are not the same thing. Copyediting often includes proofreading, but it's not its primary goal. It's the icing on the cake that makes your story better. Proofreading does not include copyediting (though occasionally a proofreader will attempt to do so and it usually means a lot of work cleaning up all their bad ideas--but I may be jaded with experiences past ;).
More tradecraft, copyediting costs more than proofreading. In instances where the schedule/budget are tight, you're more likely to see proofreading skipped rather than copyediting even though it's cheaper. Why? Because copyediting is more valuable. It doesn't just fix typos and bad grammar, it fixes holes in your plot, eliminates redundancy and cliche. It makes the story better. And surprisingly, readers are willing to accept a lot of typos if the story is good.
What does that mean? PROOFREAD YOUR SHIT! I hate reading authors talking about how bad their manuscript was when they turned it in. So and So cleaned that mess up and made it readable. Well then put So and So's name on the front cover since you weren't professional enough to make the effort yourself.
Tradecraft: No matter how hard you try, no matter how hard your editor tries, no matter how hard your copyediting and proofreader try, things will get missed. The more crap you leave in your manuscript for others to find, the more crap that will get missed. You get rid of as much as you possibly can before you turn it over. That way what's missed is minor and doesn't make you look like a writing slob.
I'm reading a book right now with an interesting premise and characters, but the frequency of errors is DRIVING ME NUTS! Complete words (articles or short prepositions) are absent in every other chapter. A) it knocks me out of the story. B) how shitty was your manuscript that you turned over that this many mistakes are present? and/or C) how shitty is your publisher that they didn't hire a quality freelancer that could find ENTIRE WORDS MISSING from a sentence.
*pant, pant, pant, pant* Okay, so the lesson, kiddies, is that a book is your face to the world. You can look like a slob and a slacker, or you can suit up and shine. Don't rely on other people to make your shit shiny. Put in the hard work. They'll think better of you for making their job easier and your readers will think better of you because it looks like you know how to write.