The primary benefit to running studs on these motors is to eliminate friction at the threads in the head. A stud stays stationary in the head while being tightened, as apposed to a bolt which is fighting friction in the aluminum threads while being torqued to specification. A stud would lessen the chances of damaging the threads, and in some cases also achieve a higher torque specification.
This, of course, becomes somewhat of a moot point after installing a steel thread insert like a Heli-coil or Time-sert. Without an insert though, I would definitely stick with a stud instead of a bolt.