A large chunk of the programming was/is either created or sourced by the regional entities, but they often need a national audience to really take off. I'm thinking of programs like "Mr Roger's" (Pittsburg), "This Old House"(Boston), "Prairie Home Companion" (Minnesota); among many others. I think those national level shows help carry the freight for the truly local shows. Apart from the national funding, so many stations on those public networks have survived by a mix of viewer contributions and discretely packaged commercials. I think it would have been very difficult for Public Broadcasting to have survived it's early years without some underpinning of financial guarantees. If it were unfunded now, it probably survives, but the programming will change quickly and only the popular shows survive.
Strictly OpEd: I've been a donor for Wisconsin and Minnesota Public TV & Radio. I believe the quality of the material usually beats the stuffing out of most commercial programming. Generally speaking, the goal is to expand viewer and listeners knowledge - that's good. i.e. I have learned a ton of useful home remodeling knowledge from watching "This Old House". Too much Khardassian style "reality" crap on commercial networks