I have also noticed the the spark plugs should be good up to 100,000 miles. I wonder if this will cause some problems when you actually replace them. I believe a broken spark plug would be frustrating at the very least and may even be expensive if it requires a special tool to remove it.
Yes I heard situations where a broken spark plug really messed up the engine, repair turned out to far exceed the cost of just changing the spark plugs.
Must be the type of spark plugs Chevy is using that allows it to last so long but if you feel like they should be changed sooner, why not?