Why do some (many?) Youtube videos not play? Very often when I click on an embedded Youtube video or even access a Youtube video though the Youtube app, I get an error that curtly says "This video cannot be played". What gives?
There is a flag that people can set on their YouTube videos to allow or disallow those videos to be played on a mobile device. What you are seeing when you try to access those videos is that the person has set the flag to 'Disallow'.