According to Us Weekly (Issue 748, June 15th, 2009):
"As Pattinson emerged in a doorway - his abs enhanced by make-up - Stewart ran towards him...."
Headline under a picture of Rob shirtless: "He's in great shape, but makeup helped."
I usually never read these magazines, but my mom got one and since New Moon was on the cover, I read it. (The article itself was pretty lame - just about Rob and Kristen's supposed romance or friendship. Who cares people?) I do not know how legit this article is, but I thought I would share it because it could very well be true. And I happen to think they did add make-up to his abs.