Boo to YT; what are you thinking?
Is that to save time?
Edit: Dumb question maybe, probably the only logical reason.
Not entirely, it also makes the videos easier to watch even if you have lots of time. A slow trickle of information just makes my brain shut down in frustration. And some people just speak annoyingly slow.
Try it on this interview with William Gibson. His slightly slurred normal speech sounds vastly better at 1.5, even though the interviewer sounds a bit rapid.
Thanks for the tip. My out of date Safari browser was not set to use HTML5 by default so I went to the following page and selected it...