While Chrome has supported HLS for a WebM backend for some time now, documentation on their support for HLS with an MP4 backend is unclear. It seems to work now as of Chrome 26, but that wasn't always the case. It also works fine on Android devices past 3.2 because of Google TV.
If I didn't happen to have a Macbook as a work PC for the summer, I'd have missed the Macbook Air announcement. But god, do I want one.
The technology is there and can be implemented: http://en.wikipedia.org/wiki/HTTP_Live_Streaming
Most just choose not to. That's not Apple's fault, nor is it a reason to fall back to a worse technology that degrades the experience for all watching to help out those on other platforms.
For the record, it wasn't at all limited to "Safari on OS X". Any device or program that properly implements HTTP Live Streaming could easily view the keynote. Apple listed Safari on OS X, the Apple TV, iPod touch, iPhone and iPad as all being verified, but other devices supported it too.
