I'm not convinced Ashley has the available funds to employ a PR agency to keep his threads alive. I doubt whether John W does, either, and even if he does, I don't get the impression that his company is the sort which uses such techniques.
I'm sure it goes on, but not necessarily in this field. The cost/reward equation for the piddling little backwater which is specialist hifi looks likely to make it uneconomic, at best, in this industry. If it happened, I might point the finger at various other, rather bigger, companies which have been known to employ aggressive marketing techniques in the past, before I point it at the (with due respect to them) tiddlers.
You dont even need a PR company. If you can write the replies yourself or have a few people in-house, you then just need the bodies to do the sign-up and posting. In this day and age, rent-a-crowd isnt problematic and also very cheap, try googling "crowdsourcing".
http://www.clickworker.com/en/ (amongst many many others...)