Does Bellard think the whole project through for days and then simply hacks it down in a few hours?
Does one of them use TLA+?
Do they use iterative approaches, where the first few versions are really buggy?
Edit: Also if you want to learn about how famous programmers work, then there's no better source than the book Coders at Work by Peter Seibel. http://www.codersatwork.com/