They got Metallica because everyone in Blizzard (at least the higher ups anyways) are huge Metalheads. I mean, they are in a Metal Band themselves (Elite Tauren Chieften is all Blizzard execs). So yea. And they had Ozzy at Blizzcon a few years back, which is an even less recent act then Metallica. As old and feeble as Ozzy is these days, he still put on a good show. Metallica generally puts on an awesome show, I have friends who don't like Metallica, but like Metallica concerts. I was born in 1973, am a Metallica fan, I do not watch regular TV anymore, haven't for a long time. Heh. But you can get the concert with the Blizzcon stream you can purchase as well, so it's available both ways I guess. Blizzard has talked about how much money they lose on Blizzcon, so I expect stuff like PPV and the Stream are attempts to recoup their losses, so putting on a big act like Metallica helps that (and I expect they are big fans besides).
Outside that, the reason Metallica actually protects their songs and trademarks/copyrights is because they actually own them. Unlike 99% of bands out there. It is really uncommon for bands to own their own music and have the ability to protect their things, it's usually the music labels who own the music. Also, Metallica didn't sue grandmas, that was the record labels, Metallica went after Napster only, not users of Napster. Additionally, they expressed regret for that whole thing (in interviews and in the movie they did), and said they wished they hadn't done it, so they quit going after file sharing after the whole Napster thing ended. Since then they have released so many free music mp3s (generally live performances, but some of it is really good), and encouraged people to spread them around.
