Yes it is. Although Islam does refer to Jews, Christians, and Muslims as all 3 being "people of the book."
Islam considers Isa (Jesus) a mere prophet, while Christians consider him God. I don't think it's be fair to say that LDS and Islam are just as Christian.
Without Judaism, there would be no Christianity, Islam or Mormonism. They're all offshoots from the same theological tradition, though they take very different approaches and interpret the "true way," or whatnot, completely differently. Mormonism is more similar to Christianity than Islam, and of course Judaism, but it's basic tenants are basically that everything known or thought of about the teaching of Christ is wrong. It's not that much farther, from this, to say that Christ was simply a prophet and not the son of god, as Muslims do.
I mean, what differentiates a Christian from a Jew? Jesus, and taking him as the son of god, and following the New Testament. Both have the same "God." What differentiates a Mormon from a Christian? Joseph Smith, thinking he is a prophet, and following his Book of Mormon. Both have the same "God" (this time Jesus).