I wouldn't call it poorly engineered, I would call it affordably engineered.

The better the system is sealed, the more consistant the engine runs. The more demanding your chosen flight program is, the more that little details like having a perfectly sealed exhaust becomes.
It's usually not a big deal to a sport flyer, but it can make a difference.

Hi Rodney
I have never had a muffler thru rod break. Every one of my mufflers has one. I make certain that nothing is ever loose on them. According to your theory, the head bolts should also break. Or the muffler to engine bolts. I have seen other people break the muffler thru bolts. They seem to be the same people who do nothing about the muffler being loose unless it falls off, once, twice, three times. The "if it does not break, why fix it" philosophy. To each his own.

Muffler designs with the through rod terminated and threaded into aluminum are prone to pull out the threads from the aluminum. Then you have to install a rod all the way through with double nuts on each end.

Actually Rodney never said anything about them breaking - his point was that when they heat up they expand, just like all the steel bolts in an engine. Steel expands a lot more than aluminium, and because the through bolts are so long that expansion is much greater than the shorter head, casing, etc bolts. When they design an engine they try to take this into account and set up torque values so that the expansion doesn't allow things like heads to come loose, but this is difficult with the very long through bolt.

The reason they don't break is because they're tightened when cold and contracted. If you had the engine at running temperature and did up all the bolts you might find problems when the engine cooled down, most likely the steel bolts would pull the aluminium threads out as they cooled and contracted. However this is unlikely to happen, as no-one wants to be playing with fasteners when they're hot.

Specialty bolt shops carry high strength threaded rod for especially problematic engines. The TT .40 Pro is famous for needing this treatment.