Until the 1990s, retraining ruled at companies like IBM. Big Blue, which promised lifetime employment to its workforce, moved its employees every few years and when it did, taught them new jobs. But when IBM’s traditional dark suits and white shirts gave way to knit shirts and khakis, the company’s commitment to lifetime employment — and thus retraining — waned. Under former Chairman Lou Gerstner, the formerly paternalistic employer laid off tens of thousands of employees. Why did the computer maker scotch retraining for workforce “churning” — that is, laying off employees with obsolete skills and replacing them with workers offering newer skills? It was simply bowing to the temper of the times, according to Wharton management professor Peter Cappelli , who says such an approach is increasingly common in today’s workplace. “In the economy now, change is faster, and the odds that your skills will need to be updated have increased,” Cappelli says.…