Yes, you are right!
Another interesting book was written by Frédéric Delâge in 2002: Chroniques Du Rock Progressif 1967-1979. He was also the author of La Boîte à Musique about Genesis.
There is as well a thesis about english progressive music: Le Rock Progressif Anglais 1967-1977 by Christophe Pirenne.
And last year, I bought a book about hard-rock/progressive/psychedelic music called L'Encyclopédie Du Hard-Rock Des 70's by Denis Protat.
It is a dictionary, with photographs in black and white of the albums' covers.