Is music streaming less threatened by piracy?

Hi,

This is rather a starting point for a debate than a post of knowledge.

I was wondering: There is a vast amount of piracy sites to download music and movies. There is also a vast amount of illegal movie streaming sites.

Why is there (almost) no illegal music streaming site? The only one coming to my mind is grooveshark but that’s basically it.

Does this suggest that streaming is somehow less vulnerable to piracy than music as a download? And if so, why?

Possible arguments are, however they don’t convince me:

Technical reasons: Providing high bandwidth for seamless streaming of a lot of music to a lot of consumers simultaneously may be too expensive in order to fund it with ads only. However, why do streaming movie sites work?

Legal reasons: Tracking down streaming sites is easier than tracking down download or torrent sites. However, again, why are there so many movie sites?

Does anybody have good arguments?