It appears that GM is recommending Dexos oil on their Ecotec engines;
From what I read so far, Dexos oil seems to be the same as synthetic oil, but with added ingredients.
According to what I read, engines wear out, and certain additives are added to the oil, to prevent some of that wear.
What additives, I don't know.
Someone mentioning that dexos oil looks slightly greener than regular oil (has a more greenish shine to the yellow), which could indicate it has certain green additives.