Why? Because different folks tend to want different subsets with their tools.
This then leads to the existence of different tools for different folks, of different UIs, and (particularly for gonzo-class tools such as Microsoft Office) various attempts at progressive disclosure and adaptive UIs.
Watch how somebody else uses Office or any other complex software; the options and knobs and paths and such can be wildly different.
If you can generalize and also isolate something specific from all the different use models (and figure out how to make money between Google Tools and open source tools and Office and such), then yes, you've potentially got something. It'll probably be domain specific, though...