Good Enough video
Internet-delivered video content doesn't always have the highest quality - but it is "good enough" for most people, most of the time. The source material wasn't always high quality, anyway: for example an old videotape of Muddy Waters was definitely recorded in standard-definition on analog video tape, and perhaps deteriorated somewhat before being digitized for YouTube, yet it is still well worth watching.
This, I think, is why the networks and cable companies are worried about losing market share and advertising dollars: these other products can deliver "good enough" content much more cheaply, and at acceptable quality.
At least the cable companies have their high-speed internet delivery pipes to fall back on; the broadcast networks are scrambling to get on the 'Net-delivery train before it leaves the station.