I live in Wisconsin(one of the reddest states on the map), but this data seems like an incomplete average. In my Leaf I average 4-4.5 miles per kWh with 3.5 on some very cold winter days and 5 on days with good weather in the spring/summer/fall. Yes winters are cold, but milder summers mean less air conditioning use than say, Florida. Also the terrain here is relatively flat with few hills and no mountains.
I think part of the problem is that there are probably only a handful of Leafs in Northern Wisconsin and the Upper Peninsula.
Krenzen Nissan in Duluth, MN does not sell the Leaf.
Eau Claire Auto Group in Eau Claire WI has a Leaf S for sale for $32,000(what a deal).
Gandrud Nissan in Green Bay, WI does not sell the Leaf.
Riverside Nissan in Marquette, MI does not sell the Leaf.
Bergstrom Victory Lane Imports in Appleton WI has 3 Leafs for sale at reasonable price and seems to be the northernmost dealer in the area who is serious about selling Leafs. So there is likely to be a lot of northern Minnesota/Wisconsin/Michigan without any data at all.
- - - Updated - - -
The Model S is much more aerodynamic. The power needed to overcome aerodynamic drag will vary with the cube of velocity.
So at high speeds having a slippery vehicle is much more important than having a light vehicle. Longer vehicle shapes are better for aerodynamics and allow the air to flow cleanly around the vehicle while the Leaf's shorter stubby stance causes more turbulence.
http://www.teslamotors.com/sites/default/files/blog_attachments/the-slipperiest-car-on-the-road.pdf