Good question and a tricky one to answer without unleashing a lot of "are you nuts" responses. I'll try to answer the question to the best of my understanding of the HDMI spec and requirements.

IMHO, I don't think there really is a difference but it is a crap shoot. Not so much with audio but with video (1080p & deep color). With that said, here's the techy info:

HDMI licensing requirements really only say that cables must be intra-pair skew. In other words, the pairs of wires within the cable must be the same. Not the different pairs (A pair & B pair) but the wires within the same pair (A1 & A2) must not be substantially different. The HDMI spec from 1.0 and up required that HDMI cables be "able" to support speeds up tp 165MHz. With the new increased speeds that 1.3 needs to carry, HDMI cables need to be "verified" for 165 MHz and "support" up to 340MHz. HDMI has indicated that they believe any HDMI cable verified to support 165MHz will pass the test for 340MHz. This has to do with "equalizer technology" requiring componments (HDTVs, etc) to have the technology enabled for speeds above 165MHz. Currently, the majority of cables are what is called "category 1" cable, verified to pass 720p/1080i. For a cable to be verifed for 1080p and "deep color" it must be "catagory 2" cable.

The bottom line again, IMHO, it's a crap shoot if you use HDMI cables that are not verified as "catagory 2" that it will carry 1080p video. More than likely it will but than again, I'm sure you've heard the stories of the guy that spent $300+ on a HDMI cable that wouldn't carry a 1080p signal from his new HD or Blu-Ray DVD player to his 1080p HDTV.