A lot of these decisions are influenced by what your income will be between now and ER. If you are going to have some high earning years at the end of your working life you may potentially be in a higher bracket in retirement than you are now. You can't predict the future but you should do your best to come up with the most accurate estimations.
I don't see the correlation between income made in later working years with income in retirement unless a pension is involved. It actually matters more what income bracket he plans to be in WHEN he makes the withdrawals. Income in working years helps people compare there current and retirement tax rates, but for most of the readers on this forum it's safe to assume a lower retirement income(assuming no pensions). Either way it matters more what the tax rate will be when the money is actually withdrawn. Financial advisors often recommend Roth to people who will be in higher income brackets when they are working, because they are not familiar with the concept of living on less in retirement.
I personally think that most MMM readers who are in high income brackets in their working careers will benefit from lowering the amount of their income in those high brackets now by choosing traditional with the expectation that they will be living a frugal retirement. The real benefit is that they will have more than 25 percent principal to build wealth from. Comparing income brackets for people who plan to be in the lowest bracket during retirement anyway becomes less of a focus, since it is likely that the traditional will perform better than the Roth in most cases(people in the 15 percent bracket are the exception).
The Roth is actually preferable to young people who have effective tax rates that are less than 15 percent. The reason being that the starting principal will be less than 15 percent lower in a Roth, but the young investor will likely see 30 or more years of compounding that can be withdrawn tax free. As the investor ages the benefit of Roth dilutes regardless of tax bracket, since the tax free appreciation is the real benefit. Roth is also useful for rich people who plan to raise there income in retirement. We call these people the one percent.
An old MMM reader in the highest tax bracket is often better off with the tax break now, since he will likely not see that many years of compounding. Conventional financial wisdom does not always hold on this forum, because most people plan to be in the lowest possible tax bracket in retirement. Traditional often wins since it can converted to Roth and be used to offset exemptions and standard deductions. The Op is the main exception to this rule. Young and still in the 15 percent bracket.