Here is the apparent source for the cited statistics. It's based on all deaths, with 2000 census figures for population and 2005 mortality data. Death rates are "age-adjusted". I'm guessing that's an important part of why MA is so low on the list.
http://www.statehealthfacts.org/comparemaptable.jsp?ind=113&cat=2
Notes:
Age-adjusted rates per 100,000 U.S. standard population. Populations used for computing death rates are postcensal estimates based on the 2000 census estimated as of July 1, 2004. Since death rates are affected by the population composition of a given area, age-adjusted death rates should be used for comparisons between areas because they control for differences in population composition. Data are for 2005.
The July 1st 2005 population estimates for Alabama, Louisiana, and Mississippi do not reflect population changes that occurred after Hurricane Katrina on August 29, 2005. The populations of these three states and of Orleans parish in Louisiana, Baldwin and Mobile counties in Alabama, and George, Harrison, and Rankin counties in Mississippi were reduced following Hurricane Katrina; East Baton Rouge parish in Louisiana had an increased population. As a result, 2005 death rates for these areas (except East Baton Rouge) calculated using these population estimates will be too low; the death rates calculated for East Baton Rouge will be somewhat too high. Death rates for Orleans parish are especially affected. Alternative population estimates for these areas are being developed by the National Cancer Institute and will be available on their web site soon.
Sources:
United States Department of Health and Human Services (US DHHS), Centers for Disease Control and Prevention, National Center for Health Statistics. Compressed Mortality File 1999-2005. CDC WONDER On-line Database, compiled from Compressed Mortality File 1999-2005 Series 20 No. 2K, 2008. Accessed at http://wonder.cdc.gov/cmf-icd10.html on 8/1/2008.
Definitions:
Causes of death attributable to firearm mortality include ICD-10 Codes W32-W34, Accidental discharge of firearm; Codes X72-X74, Intentional self-harm by firearm; X93-X95, Assault by firearm; Y22-Y24, Firearm discharge, undetermined intent; and Y35, Legal intervention involving firearm discharge. Deaths from injury by firearms exclude deaths due to explosives and other causes indirectly related to firearms.
Using the same sites stats MA has the 3rd lowest death rate over all behind HI and MN SOOO as has been speculated very, very often on this site, our low numbers of firearms deaths may be more related to our good healthcare vs gun laws working.