Just because you can't see my motives, it doesn't mean they are not there. 
I don't want everything accessible through one menu. I want a whole bunch of things readily available without the incinvenience of having to browse through a small menu where pretty much every item look the same. Thus, OD+ is a perfect complement because I can put applinks there without cluttering up my desktop.
I do NOT want to put a link to every file I work with on my dock or in rightclick, so it's way faster for me to just put them om the desktop and have instant hide/show available to me.
So, you see. They do not serve the same purpose. They complement eachother with features that make my life easier.