Remember, dexos only came out in 2011, and GM offers a 5-year/100k warranty.
Meaning, there are still pre-dexos cars under warranty until 2016.
They have to honor the warranty if dexos is used in a 4718M car to the full intervals suggested by the OLM. Did GM shorten the OLM's suggestions on Corvettes and Cadillacs in 2011? If not, then you can definitely trust a dexos blend.
Of course there is cheap dexos and premium dexos oils, but at the same time even the cheapest licensed dexos still meets the standards.
Question is, would you choose Pennzoil Dexos *blend* or would you choose Walmart's ST synthetic (not dexos but does say 4718M on the back)?