Well, perhaps you understood the original question better than I did,

but I didn't see anyone suggesting that the flight be started when
the weather was threatening an early termination; only that the oral
portion be allowed to be done even if the flight had to be postponed
until later.

But starting the oral portion makes it more likely that a flight will
be made. If the ride is cancelled, there's no pressure. If it's
already started, there will be some pressure to finish it - analogous
to get-home-itis. Therefore, it's safer to just cancel if it's at all
iffy. Why rely on the judgment of the pilots to make a good call with
respect to weather when it actually happens - safer to avoid the whole
situation by cancelling if there is doubt. After all, cancelling for
weather is never a mistake, right?

All the FSDO is doing here is reducing the opportunity for the examiner
to exercise his judgment and thus possibly make a mistake. Surely
there can't be anything wrong with that? Can there?

Michael