There really isn't a good reason that an SUV should get less than 20 mpg, without towing something.
I know that some people need the towing power of a large V8 full-size SUV, but not the 95% of the people driving them.
Most SUV's can out-accelerate my old Supra, and I fail to see a need for it. my 4Runner with it's 2.4 liter 4 banger gets 25-30. It has no power, but hey.. it's a truck. I use it for hauling some stuff, hauling the occasional people, and off-roading.
Things like the Porsche Cayenne, BMW X5, and other ultra-sport SUVs are an abomination to the purpose of an SUV. If you have a family or carry lots of people, get a Minivan. They come in AWD, get slightly better economy, and are actually safer than an SUV.
And people, and there are lots of them, that go with the safety ratings of SUV's need to be shot into the sun. the "If I get into an accident, It's not ME that has to worry.. hahaha" attitudes have got to go.
most of these new SUV's are boring too. a little Geo Tracker fits the bill for more people than the Suburban. The Tracker is a decent trail-runner, good in the snow, and gets 30 mpg doing normal driving. It's also more fun with it's removable top option.
-> Steve