I think OP would be fine with a 2WD in the western states as long as he tows on paved roads when it is not snowing.
When I went shopping for a new truck in late 2006, I was told by the salesman that 2WD was not an option on the trucks, so I bought the 4WD in sig. :S... Seriously, there was one salesman that actually told me that.:R
Do I need 4WD while towing? Not really. The only 2007 2500HD Crewcab diesel trucks in stock at the dealer where I purchased were 4WD, and I did not want to special order a 2WD because that would have meant getting a 2007.5 model, which I did not want.