In my opinion there is an additional, and important, difference between Von Newmann and Harvard architectures.
In a true Harvard architecture, fetch and execution cycles can run in parallel thanks, of course, to the use of different code and data accessing paths. Using this definition, PICs are true Harvard, while the 8051 family are not.
The 8051 has different address spaces for code and data, but everything shares the same internal data bus, so that fetch and execution cycles can not run simultaneously (even using internal ROM and RAM).

Regards,
Alfredo del Rio.