Converting Traditional IRA's and 401k's to a ROTH IRA may make sense from a perspective that is often not considered.
If married, there is a likelihood that one spouse may not survive the other leaving the survivor with a "single status" tax bracket someday. Since the single tax bracket rate is higher, there is a possibility that the survivor will be paying more in taxes - even if on less income.
It may also mean that ROTH conversions that would have been advantageous when married no longer make sense. Staying in the 15% tax bracket if married is easier than trying to stay in the 15% bracket as a single filer.