I've used Metacafe as a source of porn before... just saying...
Well DailyMotion is a better source now...Their family filter is hilarious.
The reason can be of political rammifications. Maybe the government doesn't want their inhouse secrets to be leaked through such sites.
Well, It's blocked in Iran for no reason, lol.
Almost 90% of the web sites are blocked in Iran for no reason. So it ain't surprising anymore.