We run a lot of little tweaks. One of the main things that 'has to be right' everytime we upgrade is the code that is used to verify your licensed status.
I'm sure you guys wouldn't be happy if we upgraded to 3.5 and broke that
It's best to upgrade at a more stable state of 3.5 so that as little complications occur during the upgrading process. That doesn't mean that the RC or Beta vB's aren't stable or anything, but we can't ever be so sure about that.