Do you have any idea what goes into editing a printed publication? In a good publishing environment, no one editor is ever the sole person to check mistakes on any given document. When I worked at a small newspaper, people were still finding errors when the paper was being posted to boards just before being sent to the printers, including stupid little ones made by people who should know better. It's not because the people involved were morons--it's because they're humans.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.
I read most of the book. It's sitting on my desk right now. What's not clear from your post is who you are and if you have read the book. You're free to add your own review if you have a different opinion. :)
It's not "Why can't I spell lets", it's "Why can't I type it?" I make typos like everyone else. Despite what you may think, editors aren't exempt from human frailty. Indeed, I think that's the point of the review.