Quite right! The commandments version in Deuteronomy did not offer as the reason the Sabbath must be observed the fact that God rested on the Sabbath, for the version of that seven day creation story had not yet been written. So this author states that the Sabbath is to be observed because the people of Israel must remember that they were once slaves in Egypt and even slaves must have a day of rest. It is worthwhile noting that there are three versions of the ten commandments(Exodus 34:1-28, Exodus 20:1-17, Deuteronomy 5:1-21) written by several different authors over a time period of over 300 years.
So, if you don't believe the Scriptures, what exactly do you base your faith on?
And as Myst asked me, were you there? Do you know that "version of the creation account" didn't exist before it was written or that it was written after the ten commandments were given? Is there somewhere in Scripture where Moses announces that he just got a new understanding of the beginning? Why couldn't Moses appeal to "remember what God did for them" as part of why they should honor the commandment, not as an alternative reasoning? After all, according to Jesus, "The sabbath was made for man, not man for the sabbath."
The Genesis statement: "And God blessed the seventh day, and sanctified it; because that in it He had rested from all His work which God created and made." (Gen 2:3)
Exodus 34:21: "Six days you shall work, but on the seventh day you shall rest: in earing time and in harvest you shall rest." But, those were instructions, not necessarily just the commandments that God had given Moses on the first two tablets, nor is there a claim they were, according to the Scriptures.
I think what confuses you is that for 40 days and 40 nights Moses was there with God. God told him to "write these words; for after the tenor of these words; I have made a covenant with you and with Israel. And he was there with the LORD forty days and forty nights; he didn't eat bread, nor drink water. And he wrote upon the tablets the words of the covenant, the ten commandments." (Exodus 34:27-28) So, do you really believe that God had Moses write set of "Ten Commandments" that was different than the ones He gave when He Himself wrote them on the two tablets that Moses broke? Why do you believe that God would do that? But that there are other things that they were to keep, called "judgments" is evident even after the original time they were given in Exodus 20. He announces "the judgments you shall set before them." (Exodus 21:1)
Exodus 31:13-18: In here, God states to Moses that "in six days, The LORD made the heaven and earth, and on the seventh day He rested, and was refreshed" and here God says they are to keep the sabbath as a sign between the individual and God.
Exodus 20: 11: Also declares "For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it." Did you notice that there are many judgements and other things God says, other than what we call the Ten Commandments that God gave in the same discussion with Moses.
Deuteronomy: "These are the words, which Moses spake unto all Israel on this side Jordan in the wilderness, in the plain over against the Red Sea...." (Deut 1:1) "And it came to pass in the fortieth year, in the eleventh months, on the first day of the month that Moses spake unto the children of Israel according unto all that the LORD had given him in commandment unto them." (Deut 1:3)--interestingly, this happened exactly six months after Aaron died (Num 33:38).
So, when Moses is addressing them as recorded in Deuteronomy 5, he isn't declaring another reason for the sabbath. He tells them to "Keep the sabbath day to sanctify it, as the LORD thy God has commanded thee. Six days you shall labor, and do all your work; but the seventh day is the sabbath of the LORD thy God...." (Deut 5:12-4) In Deuteronomy5:15, he says: "And remember that you were a servant in the land of Egypt, and that the LORD thy God brought you out from there with a mighty hand and by an outstretched arm: Therefore, the LORD thy God commanded you to keep the sabbath day." Moses is saying that God told us to keep the HIS sabbath day. To help them remember who GOD is and what GOD is capable of, Moses told the people--remember what HE did for you! Now remember that SAME GOD commanded you to keep the sabbath. He is trying to help them see why they need to honor God, not providing a new God-given reason for the sabbath.
What exactly is inconsistent in your understanding?