Scannos are definitely quite common in scanned/OCRed books. However, there are a lot of non-scanned books loaded with typos as well. In an industry where people can self-publish you get a bit of garbage with the good. Some self-publishers (authors) don't spend the money to have their work edited, and it shows. I get quite annoyed reading news articles and other internet posts, written by so-called professionals, that are riddled with typos. Occasionally you will get an ebook like that too.