Bear with me here; my metal knowledge begins and ends with the word "metal." So Ronnie James Dio was going to be in Brütal Legend, since he's a metal legend and all and the game is about metal music. Also a metal legend is Ozzy Osborne, who was announced to be in the game this past E3. Now the theoretical drama starts (as opposed to the actual confirmed drama). It seems that Dio is no longer in the game and his character will now be voiced by Tim "Transexual Transylvannian" Curry, which is cool if you're a Curry fan, but slightly odd if you think about it, since the man isn't really "metal."
So what happened? Well no one is officially talking, but the fine fellows over at SpineLanguage have connected some dots involving a bit of controversy between Dio and Osborne. It seems that Dio took over for Ozzy when he left Black Sabbath, and now Ozzy is fighting Black Sabbath guitarist Tony Iommi for rights to the band's name. Iommi and Dio are also both in a new metal band together that is doing better than anything Ozzy has done in the past ten years. From these loose things, SpineLanguage extrapolates that Ozzy (or -- in their opinion -- his wife, Sharon) had Dio taken out of the game.
If you ask me, that sounds like a bit of a stretch, but who knows. The real issue here is that Brütal Legend seems to be in a bit of a pickle with lawsuits and dropped actors popping up. Could the two be connected? Maybe EA thinks that Activsion will have less of a case if they drop Dio, but I don't see why.