Yes, no, maybe. There is your answer.
However, a recent New York Times article does a better, although similar job, answering the question. I urge you to take a look at the article.
There is one thing clear about retirement income though. You cannot simply have a pool of money and label it for retirement and you can’t even have a steady stream of income and nothing more.
In many ways living in retirement is no different that before retirement (except your hope of increasing your income is greatly diminished). That is, you have routine bills each month and you have the possibility of life jumping up and slapping you upside the head. Financial emergencies are bad enough while you are working even when you have time to recover, but they can be devastating in retirement with no hope of recovery. Remember, your greatest risk in retirement is longevity. In this case time does not heal all wounds.
Whether you retire with a nice 401k balance, purchase an annuity or are among the fortunate ones with a pension, you need more and you need the ability to replenish an emergency fund after you tap into the balance. In other words, the budget you have in retirement and the income to support it must include something extra to save regularly. Just as when you were working; pay yourself first.
If an emergency does hit you and you have no separate assets beyond those dedicated to lifelong retirement income, what happens? Well, you may tap into your 401k, you may incur credit card debt or otherwise borrow money, or you may be forced to trim costs even cutting into necessities. None of those prospects are appealing and if you use your 401k your future income is adversely affected. If your incur debt, your budget and living standard are over the edge.
In other words, retirement income needs to be more than enough to just pay the bills and keep up with inflation.