Single-task at the speed of light for all it matters, you still never get the benefit of not closing everything you're doing just to open up the iPad's text editor.
Users don't want multitasking. They may say so - don't listen to them. They want to be able to do stuff. One traditional way to let them do stuff is multitaksing. That's why they are screaming for it now. But there is no reason why the solution that let's them do stuff actually has to be multitasking. It could be something else entirely.
The iPhone and the iPad suck if you want to do what you just said regularly. That’s certainly true. But many other traditional tasks of multitasking are handled quite gracefully right now without any multitasking.
I see a reason. Apple may want to give iTunes a competitive edge over other music apps by keeping it the only music app that can work in the background. This doesn't seem out of line of Apple's character as of late.