Remember that with many of those tools, you'll need to update
the database afterwards anyhow, and that's not necessarily a
trivial thing to do after arbitrary changes to the directory.
Really though, you do have a point that, depending on needs,
it's not entirely unreasonable to prefer the filesystem to
be the primary data store. I personally strongly prefer the
integrity constraints possible when the database manages
everything, but I can see how people might have different
needs. With changes to the files mentioned, I wouldn't use
mv (psql can rename the blobs), and for the rest, I'd pull
them out of the database, change them, and insert (update?) them back in. *shrug*