Private companies don't really fully fund their pensions, but during the period where pensions were common in private companies, those companies were expanding in revenue and headcount, so it was ok. Was.

High-risk private enterprises don't do pensions now (can you imagine a Zynga Pension Plan?). Approximately everyone has shifted to defined-contribution from defined-benefit. The problem is USPS and the fully-private companies with legacy pension plans are both in long-term decline and have underfunded pensions, but USPS is particularly large in workforce and obvious in long-term decline (and political).

Hmm yes those 1/3 of Fortune 1000 companies who do decide to prefund (which is entirely optional, unlike for the USPS) do so at average of 30% of liability. At the USPS pre-funding rate they're projected to have 73% of future liability funded by 2016.

I think you're on to something though, we should definitely require private sector retirement benefits to be pre-funded by 100%, then we can all point our fingers and say how obvious it is that the private sector is less efficient.