My guess is that it's purely a comment at the mathematics behind it.
In order to retire at 45, unless you only live on a $5,000 budget, you'll likely need a good $2MM to do so. Barring someone who has access to the ways that the super IRAs accumulate tens of millions of dollars, it's mathematically impossible for a "non-Romney" 45 year old to accumulate $2MM with a majority of it in IRAs, since you are only allowed to put in $17,000/year. In order to accumulate $2MM in IRAs with $17k annual contributions, you would need to quit your job and roll it over into a self-directed IRA to place excessively risky bets on penny stocks and long positions in options (and most IRAs prohibit owning long positions in options, usually just covered calls).
So the only other realistic way to accumulate a few million by age 45 is to earn quite a large salary, and save it - and with only $17k/year going to 401ks, you'd wind up with far more going to taxable savings.
Yes, there are ways to be self-employed with SEP IRAs, or even creating your own pension plan that you'd fund with ginormous contributions each year....but this is aimed at the 90%-95% of people who are able to retire at 45.