Because Groups and Components are implemented atop the same backend ComponentDefinition, they share some attributes that the SketchUp GUI suppresses when the Entity is actually a Group. In particular, there is nowhere that the GUI displays either the ComponentDefinition’s name or its description for a Group (a Group’s Instance name is displayed in Model Info and the Outliner).
So, although you can assign these properties via the Ruby API they are of no use except within the API. For Components, the definition name shows in both Model Info and the Outliner and the description shows in the Components browser window.