Can someone please tell me what's the difference between the structural elements in Revit Architecture and the same structural elements in Revit Structure such as foundations, columns, beams, floor, etc. Thanks.
No difference. Same families. However, different versions of Revit might offer different features about those families. For example, if you have Revit Architecture only, you might not be able to do a graphical column schedule, which is an option of Revit Structure. But if you have Revit 2013 OneBox, you can have all the features of Architecture, Structure, and MEP together.