it's not a misconception at all. if their network goes down and your site is up, you have no videos. if they choose to change to a streaming solution that lowers the visible quality of the videos, your videos will look lower quality. if they choose to overcharge for delivery, you will pay more. if their servers get overloaded, your videos will be delivered more slowly.

Quote Originally Posted by ccjax View Post
That's a common misconception. With a CDN, the content can either be uploaded to an FTP site for propagation (just like your webserver) or it can be pulled from your server and delivered via the network.The original remains on your server and you retain complete control of your content.

And a note on YouTube - their videos are Flash progressive download, not Flash streaming. The video is cached on the user's system.