If I had to take a quick guess, I'd say it's likely that Google is mirroring the content on various servers in different countries to reduce the cost of the data transfer. If there are no local servers for streaming video in a particular locality, Google can block it to avoid a big bill until they have a local server. People can still bypass it, but the people with the knowledge to do that are a minority and probably don't cause much of a problem.
Of course, I'm probably completely wrong, but I suspect a technical reason is more likely than any kind of discrimination.
Hmm. Took a quick look at the Semantic Web one, and it immediately occured to me that it would be much faster if I could just read his slides locally without watching and listening, or streaming all of that pointless video. I guess I just don't “get” this whole video-blogging thing. ;)