Hi Thom, The contribution limit you mentioned of $6,000 is an IRA. The contribution limit for a 401k in 2012 is $17,000 (higher if you are older than 50). I would like to provide you some information on how Romney would be able to accumulate so much money in a retirement plan. There is legislation (ERISA) that, among other things, prevents a 401(a) (401k falls under the 401(a) tax code) plan from discriminating. This means that the "Highly Compensated Employees" (HCE) cannot defer a larger percent of their average salary than the non-HCE average. Given how much Romney earned, I doubt this would prevent him from taking advantage of the full deferral dollar amount on any given year (1% of his salary would likely exceed the limit and usually the average non-HCE will exceed 1%). However, these rules do not allow for the HCE population to save enough for retirement (at their standard of living). Therefore, most large corporations will offer a Non-Qualified Defined Contribution (NQDC) plan to their HCE group. These plans allow for much larger contributions than any 401(a) plan and allow for the employer to match additional deferrals, but the contributions are not tax deferred contributions (tax deferred contributions can be contributed to a 401(a) plan to reduce your taxable income). To provide some detail about a NQDC plan, I refer you to this website I found that has an enrollment guide to a NQDC plan. This guide provides an overview of the way these plans work.
I am not speaking to how Romney got his money into his account, just how it could be possible. I hate to defend Romney, trust me, but most of his money in this plan is likely not tax deferred.
Thanks for all you do. You are an inspiration!