I was just making a funny. It's not logically at odds. Snail mail and the USPS "business model" doesnt' work for many reasons, mostly because they lack a true market pricing mechanism to make decisions, which Amazon does not. Snail mail might not fly on the weekends simply because snail mail is dying, and that's the USPS's main gig.
When it comes to packages, people often want their stuff as soon as possible, including on Sundays.
*Advancing the Ideas of Liberty Daily*