Bruce Willis brought it up in the Vanity Fair article:
http://www.aintitcool.com/node/32511/
"I really wanted this one to live up to the promise of the first one, which I always thought was the only really good one. That's a studio decision that is becoming more and more common, because they're trying to reach a broader audience. It seems almost a courageous move to give a picture an R rating these days. But we still made a pretty hardcore, smashmouth film."