The U.S. broadband-only home segment logged its largest net adds on record in 2018, validating Comcast Corp.'s and Charter Communications Inc.'s moves to make broadband, or connectivity, the keystone of their cable communication businesses.

The size and momentum of the segment also put in perspective the recent high-profile online-video video announcements by the top two cable operators as well as AT&T Inc.'s WarnerMedia shake-up and plans to go toe-to-toe with Netflix in the subscription video-on-demand arena in the next 12 months.

We estimate that wireline broadband households not subscribing to traditional multichannel, or broadband-only homes, rose by nearly 4.3 million in 2018, topping the gains from the previous year by roughly 22%. Overall, the segment stood at an estimated 23.6 million as of Dec. 31, 2018, accounting for 24% of all wireline high-speed data homes.

For perspective, broadband-only homes stood at an estimated 11.3 million a mere four years ago, accounting for 13% of residential cable and telco broadband subscribers.

The once all-powerful, must-have live linear TV model, which individuals and families essentially treated as a utility upon moving into a new residence, increasingly is viewed as too expensive and unwieldy in the era of affordable, nimble internet-based video alternatives. This has resulted in a sizable drop in penetration of occupied households.

As a result, continued legacy cord cutting is baked in and broadband-only homes are expected to continue to rise at a fast clip, with the segment's momentum in the next few years compounded by Comcast's, Charter's and AT&T's ambitious moves into online-video territory.

Note: we revised historical broadband-only home estimates as part of our fourth-quarter 2018, following restatements of historical telco broadband subscriber figures and residential traditional multichannel subscriber adjustments.