It's the worst in academia, but due to lack of resource or even due to a preconception that people outside of the conference aren't interested, it's something that gets overlooked way too often.
I personally am not too great at public speaking and don't relish the idea of something I was talking about slightly awkwardly being on the internet forever, so if talks were regularly being recorded at some conferences, I would probably just not submit to give talks at those conferences. Not all of us are TED speakers! I do try to make my stuff freely available and accessible in the medium I'm more comfortable in, though (written text), by writing accessible blog-style expositions, in addition to putting up PDFs of full papers.
Keynote talks are a bit different, since they're invited specifically to be big public talks. So for those, yeah, maybe it should become routine for them to be recorded/archived. Fortunately, those are also the ones that often have the broadest interest.