For my money, adding such "feature" is undesirable - its danger is people don't realize how deep copy they are making - not to mention this cannot be done well/easy if the structure has cycles (pointer loops) in it. Something that makes B/S work hard (e.g. deep copy of complex structures) should be something that takes longer for the developer to type, so they feel a tiny bit of the burden too.
If you know your data to be acyclic and really, really want to do a deep copy, then use TheEndless's function or marshall/unmarshall through JSON string:
deep_copy_obj = parseJSON(formatJSON(source_obj))
