Grossman says:
"Medical Technology:  The American medical Association says that, if you arrive in the hospital emergency room alive, the probability that you will die from a trauma wound today is half what it was just 10 years ago.  I presented this information in a paper to the annual convention of the AMA.  Although the steady progress in trauma work is not well know to the general public, the point was not at all controversial to them.  I would politely and respectfully ask you to consider the possibility that you might be mistaken in this matter."

Fabrice Czarnecki, MD, submits this:

 I am looking for references (could not find any so far supporting that statement). Even if Grossman had references, that does not mean that intentional trauma might benefit from optimal medical care (i.e., the perpetrator is unlikely to call EMS, and most urban victims of gunshot wounds are themselves criminal or gang members, and might be unwilling to go to the hospital and be reported to the Police).
See the reference below (trauma mortality did not decrease by 50%).
Med Care 2001 Jul;39(7):643-53

Mortality among seriously injured patients treated in remote rural trauma centers before and after implementation of a statewide trauma system.

Clay Mann N, Mullins RJ, Hedges JR, Rowland D, Arthur M, Zechnich AD.

Department of Emergency Medicine, University of Utah, School of Medicine, Salt Lake City 84108-9161, USA.

BACKGROUND: Injury mortality in rural regions remains high with little evidence that trauma system implementation has benefited rural populations. OBJECTIVE: To evaluate risk-adjusted mortality in remote regions of Oregon before and after implementation of a statewide trauma system. RESEARCH DESIGN: A retrospective cohort study assessing injury mortality through 30 days after hospital discharge. SETTING: Nine rural Oregon hospitals serving counties with populations <18 persons per square mile. SUBJECTS: Severely injured patients presenting to four level-3 and five level-4 trauma hospitals 3 years before and 3 years after trauma system implementation. MEASURES: Interhospital transfer, hospital death, and demise within 30 days following hospital discharge. RESULTS: A total of 940 patients were analyzed.

After trauma system implementation, patients presenting to level-4 hospitals were more likely transferred to level-2 facilities (P <0.001). Interhospital transfer times from level-3 hospitals lengthened significantly after system implementation (P <0.001). Overall mortality rates were higher in the postsystem period (8.3%) than the presystem period (6.7%), but not significantly. Controlling for covariates, no additional benefit to risk-adjusted mortality was associated with trauma system implementation. Additional deaths, occurring after trauma system implementation, included head-injured patients transferred from rural hospitals to nonlevel-1 trauma center hospitals. CONCLUSIONS: Increased injury survival after Oregon trauma system implementation, demonstrated in urban and statewide analyses, was not confirmed in remote regions of the state. Efforts to improve trauma systems in rural areas should focus on the processes of care for head-injured patients transferred to higher designation trauma centers.