No, it's not true. You are being sold. THX is only a rating system for all devices except processors/receivers. There are many products that meet or exceed the THX rating but do not have it since those companies choose not to pursue it. For a processor, there is a bit of decoding that comes in the THX surround mode in addition to the rating system. Although many non-THX processors imitate this to a point also.

But, those are quite nice DVD players and may be well worth the high prices if you can afford it. But not because of the THX moniker.