It's simple, they created a 4K cable box, but none of the programming available through any of the networks offer 4K through the terrestrial means, so they added apps as part of their offering. Not a whole lot of apps, the main ones being Netflix and Prime, not HBO at the moment. Through these apps you can get 4k HDR programming from the streaming sites, but you have to have the subscription to them like you would on a Roku or ATV. Big difference is, you do not need WiFi or Ethernet, it uses the cable coax. The 4K picture is decent and the sound is good, better than the 1080P version but not nearly as good as the 4KATV. There is a whole other conversation about the ability by cable companies to be able to offer 4K programming through traditional means, it seems that there isn't enough bandwidth to be able to achieve this.
I thought the worst of Comcast at first, I have this box in the DVR version of it because I really do not think one can truly cut the cable and get everything they want and still pay less, through legal means, than what it costs to have cable. What is nice about this, as someone mentioned earlier, is that the interface works very well with voice commands and searches. And you do not have to change the input on your TV or HT receiver, think of that complication for the wife who may want to switch from cable to Netflix, it can be made somewhat seamless with a remote like the Harmony, but when something is out of synch, the troubleshooting part is difficult for people not well versed in HT setups.
In the end, $60 a year is not that bad for this. You may have access to PPV movies and events as well. I still have a 4KATV though, cause when GoT comes out, the only way to watch it in 4K is through the HBO streaming app. I don't have to pay extra for it since I already pay it through Comca$t!