According to C.J. Date in What Not How,
ideally all business rules would be expressed by declared database constraints rather than by stored procedures, "Declarative is better than procedural!" But given a choice between stored procedures and enforcing the rules over and over in each application that uses the database (and then probably missing some cases), the stored procedures seem like a win.
Comment on Re: Re: N-tier, client/model, and business rules?
That's all fine what C. J. Date says, and I'm not disagreeing
with that. Stored procedures are good to separate the logical
view of the data from the physical layout. Which is a totally
different issue then where you have your business rules.
Stored procedures are good because of their encapsulation.
It's the same reason you use accessors to access the state
of your objects, instead of exposing the innards.