I found this part of Nate Silver's analysis fascinating.

You have to win 60 games in the regular season to have a good chance of winning the championship:

The conventional wisdom is that LeBron James will remain in Miami or return home to Cleveland. Neither would maximize his chances of winning a championship — but Cleveland, at least, is on an upward trajectory.

In Miami, James runs the risk of staying too long with a team in decline. The Heat won 54 games last year in a historically soft Eastern Conference and were dismantled by San Antonio in the NBA Finals. As if the Spurs left any doubt, a team with 54-win talent is rarely good enough to win a championship. Since the introduction of the three-point shot in 1979-80,1just one of 22 teams to finish with 54 regular-season wins has won the championship that season.

I’m not cherry-picking data to make the Heat’s case look bad. We can expand the sample to include all teams that won between 52 and 56 regular-season games. There have been 102 such teams — and only three of them won the NBA title.

Correlation is not causation, but it's still a pretty effective chart:

Here are the 60+ game winning teams according to Nate Silver's simulations:

And King James says:

But this is not about the roster or the organization. I feel my calling here goes above basketball. I have a responsibility to lead, in more ways than one, and I take that very seriously. My presence can make a difference in Miami, but I think it can mean more where I’m from. I want kids in Northeast Ohio, like the hundreds of Akron third-graders I sponsor through my foundation, to realize that there’s no better place to grow up. Maybe some of them will come home after college and start a family or open a business. That would make me smile. Our community, which has struggled so much, needs all the talent it can get.

In Northeast Ohio, nothing is given. Everything is earned. You work for what you have.

I’m ready to accept the challenge. I’m coming home.

http://pandawhale.com/post/47319/lebron-james-announces-return-to-cleveland-cavaliers-nba-sicom

Good points. Now take a look at this...

...and note that it's missing Kevin Love.

With Kevin Love, the Cavs can win 60 games.

Nate Silver is not having a good week.

The probabilities explain that, too. :)

Such math!

As the lottery shows us, sometimes ridiculously small probabilities happen.