I'm rather certain its only youtube, seeing how I can still play background music with pandora and soundcloud and spotify.
It's funny seeing people cry over not being able to listen to a video in the background, lol.
We're not talking about background music here. We're talking here about
all apps that can play video. Those videos were able to run in the background
before iOS 6.1.
Why would you want this? Some people like to play music that's embedded in a video... just because you use Spotify/Pandora/SoundCloud doesn't mean others do.
Also, it is easy for news programmes - for example. Before, you could just play those videos in the background and listen to the news - now you can't.
Finally, it's also nice for the more educative programs or documentaries, so you can
listen to them in the background.
Like you, I use services like Spotify - which I find absolutely fantastic - but it is ridiclous that Apple has removed this functionality, even when it is not important to you.
Compare it to News Stand on your homescreen: a lot of people don't use it so a lot of people don't care if it is removed, but some people do actually use it. As irrelevant news stand seems to the first group of people, this second group of people will actually miss it.