Why John used the word Logos (λόγος) is open to debate, but I think that there are two main reasons.
First, using logos ties back to the thought of the philosopher Philo, thus providing a transition into the gospel and the nature of Christ. Philo was a Jew who lived in Alexandria and whom the Stoic philosophers there influenced. He thought that God's perfection did not allow Him to have any direct contact with the world, so that He had to have a mediator. Philo believed that this mediator took the form of an inferior god, the Logos, who was the link between God and man. By using the word Logos in John 1:1, John indicated that Jesus is the sought-for Mediator. By declaring that the Word was with God and was God, John transitioned into the true nature of Christ by showing that Jesus was not the same as Philo's conception of the Logos.
Second, saying that Scripture was with God and was God in the beginning is not what John was trying to convey, and is therefore insubstantial. John is the only writer in the New Testament to use Logos in such a fashion, and he does so in four places: John 1:1, John 1:14, 1 John 5:7, and Revelation 19:13. These verses indicate that Christ is the Logos, not Scripture itself. Using the word Scripture in John 1:1 obligates one to use "Scripture" in 1 John 5:7, thus "...the Father, the Scripture, and the Holy Spirit; and these three are one." and also in Revelation 19:13, thus that He who judges, makes war, whose eyes are a flame of fire, and who has many crowns, must also have the name "Scripture". Rather this Person is the Logos, the Mediator between God and man and God Himself. Note that Hebrews says that there is one Mediator between God and man: the man Jesus Christ.
Note also that John was written for the Greeks as well as the Jews, for John explains many Jewish words and concepts.
My sources are the several excerpts from Bible scholars including Marvin R. Vincent, Hugh R. Mackintosh, and Frederic Godet contained in the website http://www.bible-researcher.com/logos.html, as well as the Bible study on the book of John titled "Be Alive" by Warren W. Wiersbe.