The first explanation--milder economic shocks--has seemed less persuasive following the events of the late 1990s and early 2000s. From the Asian financial crisis to the September 11 attacks to the corporate governance scandals to the surge in oil prices, powerful economic shocks have marked the past few years. Yet, the economy has performed rather well, on balance, over this period.
As for the second explanation--better inventory management--changes in inventory dynamics have indeed contributed significantly to the reduced volatility of GDP growth. Those changes are consistent with anecdotal evidence and case studies about the use of information technology and better inventory management practices to catch incipient inventory overhangs before they become a problem.