I don't know about traditionally published books with lots of errors, but yes, it is common among indie books that there can be far too many spelling and grammar errors. I understand why that often is, but no that doesn't have to happen.
After I finished writing my last book, I got four people to help me hunt for the errors. Yeah, its a lot of work, but I think that if we want to be taken seriously we have to do the work.
Sure, even a traditionally published book will sometimes have one or two mistakes. It's true.... But we should be aspiring for as few as possible. It really draws the reader out of the story, and reflects poorly (my opinion) on the industry/movement.