Not true, if you turn the light control switch toward you you will turn all "automatic lights" off, this includes the DRL. I have a 2007 and it does it as well, not just a 2008 feature.

 

My 06 allows me to drive with NO lights on. I just rotate the MF(multi-function/turn signal wand) outer switch towards me, and the DRL's turn OFF. The DIC tells me they are off. I have to do this every time I start the car.

why do I want to do this? because it seems very common to see a newer GM car with at least 1 DRL buerned out. replacing bulbs is not something I feel like doing just to have something I legally dont have to have in my state. having them on in broad daylight seems useless when I am about the only car on the road with mine on. I turn them off during daylight driving.

 

Its different for canadian models. I tried it yesterday, cant turn off the headlights at all. I was trying to see how it looks with just the amber driving lights, but cant do it. The only time the headlights are off manually is when in park. I think it says so in the manual. You may need a reflash of the BCM, just a guess.