Now wait a second, maybe the author's manuscript was correct and the editor changed it? You have no idea what the manuscript looked like before it got to the editor.
I also think it's presumptuous to assume it's solely the writers fault, especially when it is the editor's job is to catch all the mistakes and correct them. Maybe the writer did make a mistake but so did the editor. They don't get a "it's the authors fault" cop out when they are paid to make sure those mistakes aren't there.
One thing I do know is that sometimes people believe a word is spelled wrong when it is not. On more than one occasion someone has pointed out a word to me that they think is misspelled and it is actually the variant (British or American) spelling of the word.
It doesn't work that way. The editor edits, then teh writers gets to go trhough the edited manuscript. When everything is done and the galley proofs are put together, teh writer then gets to go over those.
The writer always gets the last look at a manuscript, always gets to do the final proofread, so if the editor changes something the writer had correct, the writer always has the oportunity to change it back again. So no matter how the mansucript looked before the editor got his hands on it, the writer still has a chance to correct everything in the book.
Nor is it the editor's job to catch all mistakes and correct them. He does what he can, which is usually a lot, but catching and correcting mistakes is primarily the writer's job.
"It's the writer's fault" is not a cop out. It's the writer's book, the writer's name goes on the cover, the writer is, after all, the writer, and the writer always gets the last chance to look at the manuscript and correct any mistakes.
It is the editor's job to help make the book better, and he usually does, but he's not the writer, and he's probably working on fifty-eleven other manuscripts at the same time he's dealing with yours, which means he has every right to expect you to find and correct any errors he misses in your manuscript.
If you want a perfect book to emerge from the press, you must take that last proofread as your chance to make certain your manuscript has no errors.