Yes Rusty, that is stupid. OEMs in their quest to save weight and money pretty much all went to 8mm exhaust manifold bolts. The General has a problem with the LS and 3.6 V6 breaking the exhaust manifold bolts. Drill and tap for 3/8" UNC or 10mm would likely cure the problem.
Weight per vehicle is minor, but an ounce or 2 here and another ounce or 2 there adds up. IMHO the big issue for OEMs is material. Just the volume difference in steel between 8mm and the old faithful 3/8" and it will not take many engines and the bolt material for an engine is free. Consider how many V8 engines the big 2 1/2 manufacture every year and that becomes a big $ saving. As customers it is a huge piss off as we end up out of pocket for the repair. Even when we can do it ourselves it is the $for new bolts and time. If I have to remove bolts to replace the gasket or get to the broken bolt, they all get replaced.
My 2000 Dakota with 3.9 has a couple of broken bolts and the dealer said the bolts would be $150CDN. I figure I play the BS card on that!