Who told you gnutella specialises in music? I don't see LimeWire advertising music downloads on its website do you? I don't see it advertising movie downloads either. What it does say is not to use the programs for downloading copyright material. How the network is used is up to the individuals who use it. ie: Quality of Content on the Network (click on link)

There's ways of filtering out material like you saw. Search the forums & you can find such techniques. Rather than just coming here & bitching. Go to the pub for that.