Differences in resolution
The biggest thing during The Consumers Electronics Show in Vegas (CES) was the 4K televisions. 4K is a reference to the resolution. Current TV's (LCD/LED/OLED/Plasma) usually have a resolution of 1920*1080 pixels (1080p). The 4K versions have 4 times the resolution. Capable of displaying UltraHD content at an affordable price. These TV's sell for $1000 - $2000.
NaughtyAmerica offers 4K downloads
All very nice, but the average Joe has no real access to 4K content. Sure, there are some videos on YouTube in 4K, but most of the time it's just plain old 1080p (if you're lucky). The current HD media (BluRay) isn't officially certified for 4k content, so the only alternative at the moment is downloadable content. Guess which industry is on top of things? (pun intended).
As with almost everything in the past (VHS / Internet / DVD), the porn industry is one of the first to embrace the new technology. Now all we need is fiber to the home with a minimum of 100Mbps to enjoy the new format.