Nobody "lets" stuff slip through. Mistakes happen. Plenty of people are involved in putting a book out, and it's impossible to catch everything. Everyone hopes to make it perfect, but stuff always slips by. I've had people tell me about the typos they found in my book, too, and I have an amazing editor and one of the toughest copy editors on the planet. And stuff still got past us. A few mistakes aren't a big deal and doesn't mean quality is slipping. A badly edited or proofed novel where mistakes are on every other page is a quality problem.
And just because you don't like a book or think it's badly written, doesn't mean it is. None of us are the ultimate judge of what's good. We just know what we like. So called "bad books" got published and people are reading them and loving them. There are plenty of books out there I don't care for, but I try not to trash the author. Some people don't like my book either, have said bad things about my writing, while others have said it's the best book they ever read. And they're both right because they both have their own views on what's good. Those who aren't published yet will have people love and hate their books, too. That's just the way it is.
But for the OP, yep, I always feel a little better when I see mistakes, both in book and magazines. It lets me know that mine aren't a big deal and it happens to everyone.
