No catch. More and more online vendors are popping up with 6' hdmi cables for these prices (around $3 shipped, or 3 for $9 shipped). Companies such as Monster would try to have us believe that these cheap cables are inferior to their overpriced fluff.
A 6' hdmi cable in a typical B&M retail store such as Best Buy costs between $40-$60. The price of a similar length Monster hdmi cable varies from around $80 to over $130. Major rip offs.
edit: these cables from amazon look identical to a 3-pack I picked up from meritline a few months ago for $9 shipped. They work fine.