I'm not one to defend LeBron James too much, but I will to some extent here.
The difference with LeBron is that while he's joining another premier player, it's not like he's joining Kobe and the Lakers who just won a le or the Celtics who just won a couple years ago. He's joining a great player in Wade but a team that has been mediocre at best the last couple seasons and even missed the playoffs a couple years ago.
Also, he was never a rival of Dwyane Wade really, not as much as he was a rival of Carmelo. LeBron and Wade have pretty much always been close friends since they were drafted. Magic and Michael and Larry might be friendly now, but they were never friendly off the court (at least that I know of) to the extent that LeBron and Wade have been. You add the fact that Magic and Michael and Larry became closer friends with their Olympic experience as well, but that happened at the tail end of the careers of Magic and Bird. For LeBron and Wade, that happened after the fifth year of their NBA careers.
I agree for the most part with Magic and Michael criticizing LeBron, but I also think that the two of them using themselves as an example doesn't quite apply because of different cir stances.