I have no idea why, but sure enough the owner's manual omits the RWD car from its ratings. Apart from a little extra weight from the AWD components, I don't see what would be different.
What's curious is that in previous years, all (RWD v6, AWD v6 and the v8) were rated for 3,500lb.
In the 2010, only the AWDs (v6 and v8) are rated, a measly 2,000 lb at that.
I live more on the edge, testing the boundaries of the safety factor as long as I use the load spec chart [owners manual, section 9-22], but if you have the 2WD vehicle I wouldn't encourage you to.
Hopefully someone with more direct experience comes by and sheds some light,