Short answer: These are reference-style books (not textbooks) with reliable, useful information related to parts of the course. Because much of the information is available elsewhere, "required" is an awfully strong word.
Full answer: This course touches on many topics, including those not covered in the texts and those covered in the text but covered equally well by free resources such as man pages and web pages. The lectures will not really follow the texts. Nonetheless, many students benefit from having a centralized hard-copy source of information. As reference books, the course texts should also prove useful in many parts of the CSE curriculum and even after you graduate. These are good books to have, but they are a bit expensive considering how much of their content is available via other means.