It may be technically illegal but unless there is a loss of income it isn't important enough to issue proceedings. In context this is closer to “fair use†than copyright theft anyway.
http://en.wikipedia.org/wiki/Fair_use The purpose and character of the use, including whether such use is of a commercial nature or is
for nonprofit educational purposes;
The effect of the use upon the potential market for or value of the copyrighted work.
This is a “private performance†made public by posting it youtube. Not a public performance per se. It would be interesting to hear two lawyers fight over this whether it was public or private lol.
If a copyright holder was trying to claim a public performance royalty fee from amateurs on youtube, that would be pretty pathetic. Stupid also because the legal fees would be more than alleged loss of earnings. I used to work for a law firm years ago. It's all about money. You must choose your battles because it is not free to prosecute.
Youtubers playing their current pieces on youtube are far from a threat. The publisher could simply ask them to take it down. This isn’t a big deal in the scope of things but really has this ever happened? It would be crazy and shameful if it did.
Those people who have free lessons with a link to their websites selling (thus making money) a Dvd of the tutorials of pop songs (Justin Timberlake, Rihanna etc) should expect trouble as this is clearly making money from other people's work. This is theft. No defense.
The videos that media companies clearly have issues with is when people put up episodes of Tv shows that in the future will be DVD box sets. Episodes of Leno, Letterman, Oprah etc seem to be monitored closely because they sell them on Itunes. This is where they are focussed at, not people playing Yann Tiersen.
Imagine Youtube 100% legit.
All that would be left is a few teenagers or crazy people yapping on about Britney etc.