Microsoft copies Apple’s workgroup manager Icon. Details Here.
But it seems both Microsoft & Apple are customer of IconFactory.Take a look here: http://iconfactory.com/design/clients
Neither group designed their own icons and most of the work was done by the same company, IconFactory. Since this single company is creating for both OSes, we have reason to believe that both will look similar and neither is copying.
Eventhough…Microsoft has changed its icon now…