What is your definition of Christian, then? I thought if someone believed in the divinity of Christ and accepted his teachings, that was enough.
By a broader definition that you present they could be included, but there is a lot more that the majority of Christendom has in common, primarily because it uses the Bible as the primary reference source for constructing its theology whereas Mormonism uses first the Book of Mormon and references the Bible as a secondary source. When in conflict, it is the Book of Mormon that is seen as the more reliable, clear source of truth.
Joseph Smith was a Mason and also studied White Witchcraft, and he was also a science fiction writer from what I understand. A number of the temple rights and blessings are taken from these sources and the structure of the religion places humanity on the same level as God the Father and Christ and Satan (who are brothers), except that we are at an earlier stage in our development. God the Father was once a human on another planet (I think there are sources of early Joseph Smith writings that name it as "Koolag"). He lived up to his calling, married, and now has a planet of his own which is populated by the spirit children he has in Heaven with his wife. Humans procreate to make the vessels, and the spirits come down from Heaven, each one choosing which body they will inhabit. If an individual follows all the commands of the church, is married in the temple, then that union is set for all eternity and that Mormon man will one day be a god of his own planet populating it with the spirit children he has with his wife.
In Biblical Christianity there are numerous interpretations and theology, but God is seen as sovereign, omnipotent, omniscient, and humanity serves God. There is no eventual equality. That difference in the concept of God and man, along with the Bible vs. the Book of Mormon as the primary source of scripture is what creates a marked distinction.
If there are any Mormons on the board that can point out any inaccuracies in my understanding, please do. It isn't my purpose to insult or communicate anything incorrect. This is my understanding of the religion based on discussions with Mormons, but I encountered the ideas as an outsider which is different from understanding it as an insider.