More probably that the detection of parcel packages is machine-driven and based on thickness.

I don't know why everyone is up in arms about this. The Indiana people had a problem (how to get the letter mailed via the service they wanted) and solved it creatively.

This is called a "hack", not "bureaucracy". And we should applaud it. Is the rule dumb? Yeah, probably. But it's hardly alone in the world. For every styrofoam cube there are a dozen people putting letters into boxes needlessly, and that is the bad thing. This is cute.