Wow, this is pretty extraordinary. The value of assets set aside for these people may be taxable income (see section 83 of the Internal Revenue Code -- and implementing regulations -- regarding "substantial risk of forfeiture"). Most people aren't willing to take that tax hit, preferring to accept the usually low risk of loss of an unsecured pension in exchange for tax deferral until the benefits are actually paid. This move suggests that the risk of loss is higher than we might want to think. In bankruptcy, unsecured non-qualified pension obligations rank no higher than other unsecured debts to creditors.
Bruce