If, as is shown in this diagram, PR enclosed all communications and marketing activities, then it acquires commercial significance at a stroke. A logical case for this is also apparent: since all marketing activities concern publics, then Public Relations is the natural sphere in which those activities should be managed. For this to be refuted, marketing would be forced to make the bizarre assertion that its activities do not concern publics! Seen this way, only a small portion of the PR activities are indirectly commercial.
To me, the following configuration is an obvious solution to the problem of ascertaining the role of PR in revenue generation:

A: corporate advertising (promotion of the brand, not a specific product)
B: direct marketing and sales promotions (e.g. e-mail and freebies, respectively)
C: distribution, pricing, and product development
D: corporate PR (internal communications and public affairs)
E: marketing PR (publicity and sponsorship, i.e. traditional public awareness activities)
F: mass media advertising (traditional advertising)