Part of the problems with defined benefit plans are deliberate over-promising to keep workers on the job when sales are good, as with GM, and managerial starving of pension funds when they have the chance. (1) Any time the fund approaches what is theoretically 100% funding of liabilities, they want to cut funding, and often can, depending. When the stock market is 14000, they quit paying into the fund, or try to. When it dips to 8000, they whistle Dixie, disavow responsibility... demand benefit cuts to stabilize the plan... When the market goes back up, well, they have reason to reduce contributions, right? The plan is almost fully funded, right?
(2) Defined contribution plans are loved by employers, because they're not responsible for anything that happens down the road. You're on your own in retirement, so when the market collapses, you have to reduce the principal, the working capital, to meet overhead, shortening the amount of time your money will last. The forces working in your favor when you're earning now work against you when you're retired, and you can end up in the worst nightmare of elderly people- outliving your money...