There is no "algorithm" in the ribbon, unlike in earlier (menu driven!) versions of Office.
Unlike the menus in, say, Office XP or Office 2003, where some items were "hidden" until you used them, in the ribbon EVERYTHING is there. It doesn't try to "adapt" to you. Sure, you have to re-learn where a lot of stuff is, but that was often the case before the ribbon came out as well (because more features kept getting squeezed into a menu-driven UI that just wasn't made for a program with that many options).
The only thing that changes in the ribbon are some contextual tabs that show up at the end, e.g., when you have selected a picture or a table. These tabs are meaningless normally, so they are hidden. But they don't re-arrange themselves based on your usage patterns - they are static and don't change.