When the Xbox 360 and PS3 launched, the world was just making the transition to high definition TV sets. There were growing pains, and the feeling that it'd be years until enough people owned one that they would become mandatory. Guess that time is now.
While the Wii U - and let's be real, it's basically last-gen tech - soldiers on with component output, both the Xbox One and PlayStation 4 will only output video signals via HDMI. The Xbox One specifically states that it needs a "720p or higher HDMI-compatible TV", while the PS4's spec sheet says the console only outputs via HDMI.
Most of you - especially those who will be early adopters - are probably fine. Wondering what all the fuss is about. But there are still plenty of people gaming on CRT TVs (there were even CRT HD sets), and some (we've got someone on staff) who have a HDTV, but an older one which only accepts component cables.
On the downside? There are people who aren't just going to need a new console, but a new TV. On the upside? With HD being mandatory, we won't get a repeat of those problems where some people couldn't read the text in certain games.