Seems to me that the difference in behavior between banks and the post office is somewhat other than what's been discussed above.

They march to different drummers. The people who oversee banks are the government, so to speak. Someone at a medium-high level, either at the terrorist bureau (the name of which I disremember just now) or at the bank regulation boards (ditto).

The post office is, theoretically at least, a separate corporation, not a part of the government at all. They supervise themselves, and no-one there saw any necessity for such caution, and I suppose there was not a preexisting procedure in the law for government bureaus to regulate them on this sort of a detailed basis.

Dave Oesterreich