They state that bug reports from the DPs get reviewed by engineering while those from the PB get screened by a separate group. One can guess that the latter are just counted up and will never get feedback to the submitter and likely will never be seen by engineering unless they get thousands of identical reports. If you have 1,000,000 public beta testers and each submits just 10 bug reports, how many employees will take how many years to check them all out? (Sounds like a good math problem!)