I don't want to scold this PIC application, I find it great and would
    like such an instrument myself. BUT I am at home in analog circuit
    design and have seen lots of times what overvoltage can do to
    circuits, and I have not always seen what I liked.

Lack of adequate protection against extremes in input voltages seems to be
fairly typical of "non-professional" designs, especially in circiuts where
the "typical" application won't encounter much in the way of such extremes
(logic probes and the like.)  An app-note like this is an EXAMPLE of an
application, not a safety/emi/robust product ready for use by consumers.
I haven't looked at the appnote, but I think you're expecting too much
from a design presented in that form.


    AND (and this has been completely omitted in the response) the
    positive shunt diodes connect to the POSITIVE SUPPLY!!!!! So the
    supply will get all the mA that the protection diode will protect OFF
    THE INPUT. Due to this, THE SUPPLY VOLTAGE WILL INCVREASE UP TO ::::::
    VOLTS, (whatever is applied externally), because the PIC is a devive
    which (Fortunately) does not consume such high currents.

Isn't that rather highly dependent on the characteristics of the power
supply?

BillW