Oh, and just for the sake of philosophical discussion: besides my experience of commandbars being buggy, there may very well have been some fairly core parts of the commandbars code which just didn't lend themselves to being easily ported into the new version (at which point, maybe having to revamp the entire code structure anyway, they started thinking outside of the box?)

Off the top of my head: the "taller" commandbar. When MS first came out, the height of those commandbars was almost as tall as the ribbon is now (when everyone was using 640x480). The commandbar rows have effectively gotten smaller and smaller. But there is a need for those tiny buttons to be seen by aging eyes (we're not all 25 with perfect vision). I can't tell you how many people I see, over 60, with 30 inch monitors running at some ridiculously low resolution so they can see the buttons.

And despite the ability to make the buttons bigger, they may not have been able to leverage a higher graphic resolution. So maybe they had gone as far as they could in extending the life of a user interface designed around 640x480 and 800x600 screens?

Having spent at least one part of my programming life identifying core bugs in MS Word code, I will tell you it was surprising to me what parts were fixable and what parts weren't. Sometimes the bugs are deep enough that the only "solution" is a complete teardown and re-structure (I specifically remember one where selecting a table from the bottom right to the top left, instead of the top left to the bottom right would cause erroneous errors--that MS "remembered" how a selection was made, rather than just dealing with the selection was a surprise-- and also unfixable in that version).

I wouldn't be surprised to find out that was the original impetus for the Ribbon (although all of your points would certainly add in to the discussion as well).

Cheers,
-Jason