More likely streaming music services have various agreements which only allow them to operate in select countries. I recall that when I was visiting Canada in 2010, I had to proxy my traffic back to the US to use Pandora.
It is not up to countries to enforce Pandora's contract though.
While this is true, I (in Canada) can still go to pandora.com and I just get a message saying that the service isn't available in my region.
They don't. It depends on these services having agreements to sell their business in China. And FWIW they can always use QQ music which is pretty much most Chinese use anyway.
Yes. It is not related to political reasons.
How do you know? I know they blocked YouTube and liveleak for political reasons.
You can access those music sites fine, it just shows "not available in your country". Adding music sites to the list is a good nice "side-effect" to use these service since most of proxy exits are US based.