Because when you are streaming music from another server (like a website) you aren't actually using the Graal servers at all, you just use a music client (in this case, Graal4.exe) much like iTunes, WinAmp or Windows Media Player. You think those programs have to pay royalties when they stream music from a site?
And second: Yes, I'm pretty sure you won't be able to ever use the stuff you use on Graal anywhere else. Ideas are a immaterail and are hard to make lawsuits over but actual files such as songs, scripts and images are very obvious. If you plan on using Graal as a stepstone for "things better" I suggest you just use ideas you wish the develop; as the the material things: just make stuff you are content keeping on Graal. You
could ask Unixmad if you could "loan" the files but in such a case, I doubt those files would be allowed on a non-monitored playerworld (any non-gold server).