I'm not quite as PC-illiterate as you seem to think... I've been using menu keyboard shortcuts (with ALT to open the menu) for years, far before the ribbon existed ;)
The issue is that in older menu-based UIs (Office 2003, OpenOffice) the keyboard shortcuts very often lead to UIs that are no longer keyboard-navigable, or require the use of the tab key (multiple times) to navigate through a bunch of checkboxes, drop-down lists and so on. Also, many of the options don't actually have a dedicated shortcut key...
For instance: In order to change certain formatting aspects in Office 2007+, I can use keyboard shortcuts to access anything visible in the home tab of the ribbon. In Office 2003, I have to open Format=>Font (which is accessible via a keyboard shortcut, like you said), but then I need to either tab around a lot to select checkboxes and drop-down lists or just use the mouse.