Is cable that common? Assuming you mean cable tv, it seems that at peak it was only just over half of all homes that subscribed and is falling. Presumably this is due to Netflix et al. However wiki numbers stop a few years back.
The point about it being hooked up to a cable box isn't particularly relevant unless you're only watching OTA digital TV all your media comes from what can be roughly described as a computer attached to a monitor. And even if you are just watching digital OTA TV any relatively modern TV will have an HDMI port.
Even without cable boxes, basically every TV has an input you can plug something into, even if you've got one of the extremely old ones you can get an adapter.
https://en.m.wikipedia.org/wiki/Cable_television_in_the_Unit...