I also thought the same as you guys, the THX meant that the products were just certified, a kinda thumbs up sales tool, I own a well known eletrical retailer and was recently invited to a private seminar in Surrey, where we met the guys at Lucasfilm and the designers behind THX Ultra2, believe me, i was completely wrong, THX means so much more then passing a test, the additional technology required in THX certified products is huge and the list of benefits endless.
I believe that this is one thing THX (lucasfilms) have got amazingly wrong, they have not promoted what THX is all about, just that it means it's good, a recent survey showed that a third of the population in USA, UK etc recognised the THX logo, but know one know what the F*** it means.