In 2001, the New York Marathon took place 54 days after 9/11. The fires were mostly out by then.
Having the marathon on Sunday is more like having it a few days after the hellacious snowstorm of 2010. You might have been able to clear the streets for the race, but what about the streets you weren't plowing. How much money would be lost by those people not being able to get to work? I think you're looking at a much higher cost than the revenue a sporting event brings into the city. Penny-wise, pound-foolish. It's probably more money to get the bodegas and delis open all over the city. And the barber shops and halal food vendors. And get some more trees off people's houses. Re-open Central Park for the people. So totally like the mayor to focus on opening it for the media and elite runners. The city needs the park. And what about people with no electricity. Give me a break.
Another comparison. The Yankees returned home on 9/25/01 -- two weeks after 9/11. The baseball game involved a small part of the Bronx which was far from the disaster, and all transport systems to and from the Bronx were working at the time. Most of the infrastructure of the city was unaffected by 9/11. Not true in 2012.
More prior art. The Bay Area World Series resumed ten days after the Loma Prieta quake in 1989. As bad as that was, and it was really bad (I was there), this is a much bigger disaster. I don't think that's sunk in with a lot of people yet.