“Proprietary” as a positive selling point?

Why is it that companies use the word “proprietary” as a selling point?
For example, a big shipping company has a partnership with the US Postal Service to provide various package-management and expedited-delivery services (( Mostly by moving the package through their own network to the post office closest to the recipient, then handing it over to the post office for last-mile delivery. Why this is better than sending something entirely by UPS/FedEx or entirely through the post office, I don’t know. )) and, as part of the list of things they claim make their service better, they mention “proprietary software”.
Other companies mention proprietary formulas, methods, etc.
Do people usually think of this as a positive thing? Maybe it’s my background in science (essentially all discoveries go through peer review and are published for all to see) and being a bit of a free software geek, but I don’t see proprietary things as a good thing.