A reader writes:

Romney was probably the beneficiary of a profit-sharing type retirement plan, which are often set up in small companies in which a large portion of the employees are well compensated.  The total contributions limits in this type of plan are fairly generous, close to $50,000 per year in a combination of tax-deferred and non-tax-deferred contributions (see here). If those contributions were in the form of stock, they could have appreciated rapidly. For example, 20 years of contributions at $50K per year would add up to $1 million, and if that was in the form of stock that appreciated by a factor of 20, it would now be worth $20 million. While that money was originally in a profit-sharing retirement account, Romney could have rolled it over into an individual IRA when he left the company.  That could well explain his very large IRA balance.

A "former private equity executive" writes:

As this WSJ article points out, public pension funds are major investors in private equity funds.  The article details how pension funds (which manage hundreds of billions of dollars) now allocate 11% of assets to PE as opposed to 3% a decade ago (when Romney left Bain).  These small allocations for the pensions still mean billions of dollars allocated to the PE managers.  What the article misses is that these pension funds were invariably the largest investors in PE funds in the 1980s and 1990s.  So it may well be that Bain Capital’s business was built on the backs of public pension funds.

So when Obama/Warren point that no business is built without some government assistance (roads, Internet, etc.), there’s a gotcha out there when Romney/Sununu talk about the American style of business building.  Page 83 of this pdf of the Massachusetts Pension Reserves Investment Trust Fund 2009 Annual Report lists several dozen PE firms that manage the pension’s money, including Bain.  These kinds of pension fund – private equity relationships go back many years.