I think it has to do with the lease cash that NMAC is offering which is based on the customer's ZIP code (where the car will be parked overnight). Certain areas of the country are being incentivized with larger lease rebates hence the better deal. So buying in WA (or similar incentivized states)...
I think that I got a pretty good deal on my new Leaf.
2012 Leaf SL - Glacier Pearl
24 Month Lease
12K Miles/Year
$180/Month (23 payments)
$0/Down
Sales tax exemption in WA state
I should be able to make the lease payment with the gas savings alone.