There are many protocols, including HTTP Live Streaming, RTSP, RTP, MMS, used by multiple browser plugins, such as QuickTime, Flash, Windows Media Player. A comprehensive list of such systems is on Wikipedia: http://en.wikipedia.org/wiki/Comparison_of_streaming_media_s...
Twitch uses HLS with a Flash front end. No idea about the others.
HLS is nice because it doesn't require any new servers or protocols -- it uses vanilla HTTP, and can be served up by basically any web server. As a result, it's much easier to make it work with a CDN.
I guess the reason of having such poor support outside Apple browsers, despite the benefits, has to do with licensing issues and the complications of embedding ads, as someone pointed out.
Twitch, Google Hangouts, any "live" sport event what protocol/technology do they use ?
A mix of HLS and flash ?