I mean, it's a nice theory but it isn't actually true. There's tons of functionality which exists in many ribbon-ified programs but not actually accessible from the ribbon.
If you right click on the ribbon in many applications and select 'customize' you'll find all sorts of useful functionality. The customize window (at least in Excel 2010, which I happen to be looking at at the moment) has organization to help you find the stuff you can customize the ribbon with, and it even has a 'commands not in the ribbon' section!
Maybe the ribbon contained all functionality when it was first introduced (though I doubt it very much) but that certainly hasn't been true for years.
It's even worse: look at the Paint in W7: there is a ribbon, but try to find something as simple as "print" there. No, the Print button is behind the button that drops down the menu. Then look at the Mail in W7 (Live, whatever). Once the big button called "Send and and receive" on the toolbar is also not on the ribbon, but a tiny tiny button on the title bar. If you already have the muscle and visual memory for the older interface, such "illogical" shifts can remain confusing for a long time. Especially to the older people.
If you right click on the ribbon in many applications and select 'customize' you'll find all sorts of useful functionality. The customize window (at least in Excel 2010, which I happen to be looking at at the moment) has organization to help you find the stuff you can customize the ribbon with, and it even has a 'commands not in the ribbon' section!
Maybe the ribbon contained all functionality when it was first introduced (though I doubt it very much) but that certainly hasn't been true for years.