[duskwuff]

Perhaps the content owner is making ad revenue having their content on Youtube, and won't get that revenue from the mobile app. Or perhaps they plan to launch a mobile app of their own at a later date, or license the content to someone who might.

Point is, you can't go assuming that just because something's available on the Internet, you're free to make use of it however you please without so much as asking. That's just plain rude.