There are a couple of differences between Deut. 5 and Ex. 20 besides the slight rewording of the commandments. Exodus includes Aaron, Deuteronomy does not. Also, in Exodus the people seem to want to come up the mountain and Moses warns them away. In Deuteronomy the people are scared, although they do hear the words God speaks. Those seem to me to be important differences of emphasis--particularly with regard to how special the priests are.
With the greatest commandment, formulated in the NIV as--Love the Lord your God with all your heart and with all your soul and with all your strength--it seems to me that we return to the idea of YHWH is the best god, rather than the only god. That could just be that it would be cumbersome to keep saying, "don't worship the other gods--which are fake gods--because out god is the best god and the only god."
Finally, we have the genocide mandate. Like with the stories about killing the man while having sex with a non-Isrealite, we have modern equivalents of invaders indiscriminately killing current occupants of land and destroying the culture. Now, I believe this is a story to establish Hebrew purity and to deny a mixed ancestry rather than literally instructions that were about to be carried out. Still, it is heart breaking to read in the holy text.