The biggest problem with the old style menus was the number of "features" they try to represent. each menu was becoming too long, with many submenus. I believe that microsofts testing shows the average number of clicks to get to any specific item drastically decreases using the ribbons. (although a minimum of 2 clicks to do anything is quite annoying - select which ribbon, click the thingy. Apart from a few esoteric examples above (which don't quite have any good place to go under the new scheme, although i suspect there are better ways to get at whatever is wanted under document properties) everythign is in a good place under the catagories listed, with the most commonly used items big and in the top left corner. (and no, they don't randomly shuffle themselves around in my experience).
RE: "These experts seem to believe users actually READ all the options" -- for commonly used options they don't, but for the one time a year you want to remove duplicates from an excel sheet (actually found in a logical place under data tab, data tools group) people do read through options until they find what they want. The new ribbon layout makes that operation (find the random button you know is there somewhere) faster, at a slight cost to power users who don't know keyboard shortcuts, who take a single extra click to get to where they want, if the operation they are doing is of a different type to the previous one (want to conditionally format that new column, then click home, click conditional formatting, click data bars, click the blue bars).
http://blogs.msdn.com/jensenh/archive/2008/03/12/the-story-of-the-ribbon.aspx gives a good overview of why microsoft went the way they did.