The down side to using bolts instead of studs is the wear it puts on the case.
With studs you put it in the case once and then you can take the nut on and
off the stud many times and then if you replace the stud you would take it out
of the case and put a new one back in.  Maybe if you went through alot of
studs you would put these in 4 or 5 times in the entire life of the vehicle.
But when you use bolts every time you put the bolt in the hole and take it out
you are putting some wear on the case.  So you remove and replace the exhaust
system, then you have to do the head gaskets, then you do the exhaust again,
then you rebuild the motor, each time you remove that bolt it wears in that
hole.  That is the real difference.  The clamping force if the same and as the
fastening quality goes they are the same.
Ken Wilford
John 3:16