Every country's postal system is a system with a lot of interacting parts. You change one part, and it affects the others. Our postal system makes extensive use of mail delivered by vehicles directly to mailboxes that are located at the curb, on streets that are relatively dangerous for people. [0]
[0] I couldn't quickly find any believable stats, but I think it's a reasonable guess to start with traffic deaths in general, for which there are published numbers.
The first part (mail directly to mailboxes) is the same everywhere I've seen it too here in Europe (mostly Spain and Sweden to be fair). But yeah, the second one makes a lot of sense. Would actually explain a lot of the design choices for anything American. We don't have that much to worry about, so we can spend less on armored postal vans.
There's relatively few countries in the world that are as large and sparse as the US. Sprawling metropolis's are rare. In the rural areas, houses are miles apart.
