It's definitely worth getting excited about though, it does half the bitrate usage a lot of the time.
I agree that such stats are exciting, but for now it's only reasonable for VOD usage like normal non-live YouTube videos.
why can't people stream in HTTP to say Twitch if they supported it?
HLS and DASH (both HTTP-based streaming methods) are specifically designed to work like this: The server hosts video (the video lives on the server's hard drive somewhere), a user who wants to watch the video sends a request for it, and the server sends to down. So
the person receiving the data has to initiate the request, and
the server that sends the video has to support receiving HTTP requests. That model doesn't work if you're a streamer trying to send data up to the server rather than download from the server, since it would require the server to request video from the user rather than the user pushing video data, and then the user would have to have their computer configured to serve HTTP, which often isn't the case without setting up things like port forwarding on a network.
RTMP servers are instead set to
listen for connections, and users can then initiate and push data without the server requesting it. Then it can also respond to other user requests for the video and pass it along to them, often without even needing to transcode, which is why raw RTMP has such low delay compared to HLS.
As for RSTP, I admit that I'm not very familiar with it (I do know it's an older technology), but from what I understand, it's designed for different purposes than the kind of streaming we're used to with Twitch.