We can deliberate over the meanings of terms all day, but there is a distinction. The PBS commercials are just "this company supports PBS"; it doesn't even mention the industry the company works in. Commercials elsewhere are "this company makes this product, which does this task that will make you happy and/or surround you with beautiful women".
Do you think these companies would keep giving PBS money if they stopped reporting who was giving it before/after each show?
Also your claim isn't even true, I recall an ad for a European Boat Touring company before Rick Steve's Europe for example. The ad was clearly "this company sells this product."
It's all just another form of lifestyle ad / virtue signaling. "We support PBS and the things you care about, support us too."