On all the Android devices I've ever had, I've never seen one that could actually allow flash music streaming or YouTube to run in the background on a minimized window.
For example, if you are on a music streaming website, as long as that web page is in the foreground the audio will play. However, if you need to minimize that window and open another tab, for example, the flash stream stops.
It's the exact same way for YouTube; as long as the video is open in the foreground window the music will play.
Is there any way to put those in background, but have their sound continue to play?