"IBM could spend some bucks to get rid of older employees by offering a decent retirement package. Problem solved. Young g-ns take over, the natural progression of life. Hundreds would voluntarily retire. "
Pension plans were originally used as an enticement to join a company. They were first used by the government to encourage people to join the military way back (and still are with a nice benefit). They became widely popular in the private sector after WW2 as a tax deductible end run around wage controls as a way to compete in a tight labor market.
However, a widely known benefit to the company was definitely a humane way to set an "end date" for older workers to retire and open up positions. Employees were happy, but defined benefit plans eventually became very expensive between ERISA which passed in 1974 and an aging workforce in companies with lower turnover.
IBM got rid of its pension in 1999. It turns out, apparently, it's much less expensive to tell someone 50+ not to let the door hit them on the way out. That includes the measly separation payment and lawsuit settlements. It's not the same as Ford running the numbers on the Pinto and determining it was financially better to let people die a fiery death and survivors' lawsuits vs. fixing the problem. But every MBA learns that financial analysis and I'm sure it's been run many times at IBM.