All the points were hit. IMO I do not subscribe to the trans fluid which is never changed. I have done extensive research on the transmission and aside from the owners manual I have seen in countless places where you can change that fluid. Even here!
Unless someone else has concrete information, the most I gathered is this is a 4T60-E/4T65-E automatic 4 speed trans. Which has clutch bands like any other transmission and has a filter like every other trans which is a wearable part. I do not know if this was a designed service interval but no transmission is bullet proof and given that some examples state service, daily driving can also count for that.
It is not hard to change the fluid, it is different from past years where there is some special care needed but IMO 100k it should not hurt to flush the fluid, you never get it all anyways so it mixes and IMO would show a difference in feel.
My HHR has 21k on it and I fully plan a Flush @ 50k. Given its driven 1-5 Miles one way to work and only time it gets major milage is freeway use.
My matience over haul is...
Fluids (oil, trans, differential (if required), coolant)
Plugs (GM, OEM)
Wires (GM, OEM)
Filters (Oil, Trans, Cabin, Air, Fuel)
Brakes (inspect, replace, adjust (rear drums)
Tires (inspect for dry rot)
Battery (have tested
Belts (inspect and/or replace)
Detail (have a clean car just drives better)
2002 Pontiac Trans Am Navy Blue Metallic 12.30's @113mph
2007 Chevrolet HHR LT 2.2L Majestic Amethyst Metallic