I said it was the closest, not a price match. Take a look at the area of next day delivery service you get from FedEx Ground (or UPS for that matter, they're almost identical). Compare that to where you can send something next day USPS.
The post had 2 parts. One, that comparing $30 express service to 42c envelope service through the USPS was a useless comparison ( at least compare USPS priority services) and two, that the USPS is much slower in getting those 42c envelopes delivered than even the cheaper FedEx services, which means you have to add that value judgment into the equation.