A lot of times guys do set their sub too loud. Lots of people are "bass heads," and the first thing most guys do to show off their HT system to friends it throw in LotR or the podrace scene in "Phantom Menace." It can be risky to set up the sub by ear. If you calibrate the sub with an SPL meter, it may initially sound a bit too lean, but once you allow your senses to acclimate themselves to realistic bass, you often realize you've been hearing too much bass in the past.
I can't rule out, 3db, that the PSB sub I heard could have been damaged. It was definately set too loud, and I heard a lot of the port noise & distress you were talking about. As you mention, proper setup is key.