Barb, the gloss on covers of books and magazines is called "varnish" in the print trade. I never looked into what they actually use as the varnish. I never thought about using a cleaner on a book right out of the box. Thanks for the tip.
As an aside, the inside pages of some more expensive books, which look semi-glossy, are clay coated. Clay coated papers make for higher quality printing, but they also make books a lot heavier. My textbooks are mega heavy because they are both clay coated and oversized. It is no wonder students often use those wheeled bags or enormous backpacks. Try carrying several of those around along with other tools necessary for classes. Ouch, indeed.