It's a third party that has a contract or permission to record the videos or the technical sessions, and there is a cost, but they are well done. for organizations, they do let you post the recordings on your organizations network to share (if you by that version) or and individual can purchasing stream (lower cost). I already was notified (yesterday) that the streaming versions were available, but when I went to check it out, their "newly designed" site was under maintenance.
to purchase, the site I used (pre-conference) was Welcome to ESRI Online | ESRI Online (and no, I do not work for esri or the Sound of Knowledge ...just a user that decided that it's well worth it to see more and share the tech sessions with staff).
Although many of the slides seem to (eventually) be posted, I think that is the only way to get the videos of the tech sessions from the UC, but as mentioned, the Dev Summit sessions are available http://video.esri.com/channel/2/events and, although they are several months old (0and some things will have changed), some topics will still be relevant.