Receivers/Pre-Pros are different than amplifiers, speakers, dvd players, cables, etc... in the THX world. In this case, there is no additional processing, the THX logo just has a performance "stamp of approval" on it. If you do your homework on these units, you can get better value out of non-THX certified components. Nothing else in my system is THX certified, and that is the reason.
To say that the THX logo "has no more bearing than ISO9000 or Underwriter Laboratories" may be true on some components but is dismissive and incorrect when you are talking about a receiver. The question then becomes "Does the THX processing sound better to YOU?". If it does, then happy day! If not, then happy day!
There are plenty of good quality gear out there with both the THX logo and without. I would guess that there is more "crap" out there without the THX logo than with though
But, as has been stated above, you pay for not doing you homework.
Chromy