I guess it isn't really bankrupcy proof, but if the money no longer belongs to the company, it is safe from that company's bankrupcy.

Why not make it standard? I don't know. It is pretty common in some areas. I haven't been offered a regular pension since 1988. 401K's, IRAs, etc. are the employee's money, and thus protected from the company's problems. I might guess that the pension fund is a company asset (401K's etc. are the employee's asset, not the company's) and thus the company could borrow against it or something. It also may be that pensions are funded like Social Security - your money doesn't really exist now and current funds are going to retirees.