Actually you forgot another Ribbon, the MFC version.
There is no competition between them because each ribbon has it on purpose and users and provides a familiar programming experience for their users.
WPF provides a ribbon with XAML syntax and other WPF properties.
MFC version provides a ribbon that uses the familiar MFC object model.
Office ribbon is useful only for office add-on.
Windows 7 is used by native win32 developers and WinForms developers (using my wrapper library)
I didn't heard about SharePoint Ribbon, but I assume it has its own benefits.
Hopefully, this clarifies the mess.