Official music videos on YouTube from three out of the four major labels can’t be embedded in third party sites. You can embed Warner, you can’t embed UMG, Sony BMG, or EMI. If you use unofficial versions of the videos posted by a third party you can embed them, but not the official versions posted in the labels’ channels.
The back story is that the labels spent the last few years having a huge fight over royalties from user-driven video sites, and successfully got YouTube to pay for rights. (I’m don’t know for a fact that YT pays, but from what I know about the industry I’m sure it’s true.)
The issue of embedding has nothing to do with whether or not the labels get paid. They get paid on embedded plays. (Again, I haven’t see any contracts on this, but I know enough to have confidence).
But now they want a secondary benefit — to control distribution. Allowing third parties to embed videos from YouTube frees them from having to do 1-1 negotiations with the labels, and the labels want to be able to negotiate with each and every site that shows music videos.
I imagine the majors have three motivations. One, to be able to charge different rates depending on the site, so that they can raise rates depending on how deep the embedding site’s pockets are. Two, to be able to meet various contractual and marketing requirements. For example they may have morals clauses for wholesome artists like Hannah Montana, which would be both a legal and a marketing issue. Three, they have other negotiations in which they want to be able to use music videos as leverage. For example they might have an ongoing negotiation with LimeWire in which LimeWire wanted the ability to show YouTube music videos along with the ability for users to share MP3s. (In reality the labels’ desire there would probably be just to freeze out LimeWire completely).
Imagine a web in which every relationship had to be negotiated by hand. It would be the opposite of the internet.