This was an issue that almost prevented me from buying the H3 - but I decided to take the chance. The Explorer Sport (what I traded in for the H3) had the selectable 4WD. Honestly, I can not really see much of a difference in mileage, but then again the Explorer had almost 150,000 miles on it so the mileage wasn't as good as what a new one would have produced.
Regardless, if the research has been done, determining the 1mpg difference between the setups, I don't think I'll be losing any sleep over it. Still, choice is a good selling point and I am not sure I like big brother deciding what is best for me up-front. I always knew when I would need the 4wd...
This is likely an option that may have had underlying liability issues- i.e. some nutsmack sues GM and Hummer for an accident where the driver should have but didn't.
