The front-end developer's answer is "oh, the app can handle it. Don't worry about building the rules into the database, we don't need no stinkin' ACID compliance."
The DBA promptly explodes.
Having business rules in the app might be the way to go though for all we know. What part of ACID do you think they're breaking? The C?
Among other things. 🙂
Concerning business rules, they should be in the DB so no one can get around them. That's rather the point of having enforceable rules, right?