[Glen e]

As said above it's a marketing tool. They just want to make sure you use good, correct spec oil. If you think about it, GM does not own a refinery, nor check the oil on warranty via Blackstone or an oil analyst service, warranty costs at the dealership don't allow that expense. I.e. GM won't cover the cost of a dealer trying to figure out if your oil was dexos by sending away a sample.