On Dec. 26th, I sent fueleconomy.gov an email wondering why Volt (and LEAF) were not listed. Here is their response:
"Thank you for your email. We at www.fueleconomy.gov are not permitted to post data until it has been fully reviewed by the EPA and is formally released to us for posting. We expect to receive data from the EPA for the Nissan LEAF and Chevrolet Volt, along with other 2011 models very soon. We will probably have the data posted within a week or so. Manufacturers may release test data at their discretion which is why you will typically find the EPA estimates posted on manufacturer websites before they appear on our website."