This means that NPR cannot go around their stations directly to their audience. They simply don't have the infrastructure and resources to raise an equivalent amount of donations directly. And as a matter of preference they don't want to hurt the local stations. They like the local stations.
It puts major restrictions on their product strategy. Everything they do has to have a way to tie back to a local station, and drive donations to local stations. If they just send everyone to NPR.org, they will go out of business.
In this respect, the NYTimes is in a better position for digital. They directly own all their reader and customer relationships, so they have more freedom to innovate.
[1] http://blogs.census.gov/2015/08/13/majority-of-americans-dri...
1. All Things Considered - 13M weekly listeners 3. Morning Edition - 13M 6. Marketplace - 9M
Cue well-polished NPR briefing
Do you not feel patronized when one news outlet claims to be the ONLY one you need? Part of being a responsible citizen these days is seeking out a range of sources.
"This program is brought to you by -insert brand name, followed by slogan of the brand-".