Not true. Sorry. In the first place the studs are not typically "threaded securely" into the aluminum castings. They are often only finger tight from the factory. As for your theory that the bolts are being threaded in at high preloads, if you torque them correctly and don't over do it as is too often the case, you are in no danger of damaging the aluminum threads in the casting. Where people get into trouble here is from tightening the fasteners too much and too often. As for "repeatedly" tightening, why is there a need for it? Unless you are constantly tightening, which is a mistake, you're not adding any wear to the aluminum threads. The factory studs and even the nut, which some people say are junk, will suffice if installed correctly. The weak area I've seen are the kit supplied lock washers which flatten too easily and do not function as locking devices after the initial tightening. If you're going to replace the fasteners always replace the lockwashers with good quality items. One of the problems I see on every engine I've delt with is a uneven mating surface between the head of the bolt or nut where it tightens against the intake and exhaust manifolds. The weld bead often extends into this area which prevents the undersurface of the bolt head (nut/washer) from having a full contact surface. This will cause the bolt or nut to be cocked when tightened against the flange which can weaken and cause failure of the stud or bolt under stress (vibration) Don't believe me? Check your exhaust and intake manifolds where the bolt head or nut tightens against them and look for a flush fit. If there is any interference between the head of the bolt or nut with the weld bead you have the potential for eventual fastener failure no matter what you use, grade 5, grade 8 studs and nuts or Allen head bolts. All of this is also true of the engine mounts. There is absolutely no need to tighten and retighten these fasteners over and over again. Use good lockwashers, tighten once and then again after the engine has reached operating temperature the first time then visually check them for flattened lockwashers. If the offset ends of the lockwashers are not aligned then the fastener has loosened if they are flush, nothing has come loose so leave them alone. Pepeated tightening is the biggest cause of fastener/thread failure with these engines. Not poor quality fasteners.
Tom