The media loves this stuff, to be sure, but established modern police strategy, as part of the Broken Windows theory, is that highly visible disruptions of the peace, like gangs of thugs overwhelming a poor shop owner and robbing the hell out of a store with large numbers, need to be stopped lest it create a larger climate of crime and motivate other criminals.
Whether there are a lot of these incidents or not, stopping them is very important to curb a culture of lawlessness. And to preserve the good name of actual flash mobs, which, while SO over, are harmless fun.
I hate the various music industry groups as much as anyone, but I hope they win this battle. The vast majority of lyrics sites are riddled with some of the worst advertising you'll ever see, and worse, many of them feature dishonest spyware advertisers and popups. The music industry should wise up, start their own site (with ACCURATE lyrics), and sue the lousy sites out of business. We'd be better off without most of them.