Blinky,
I'm not an accountant or an actuary so I might be looking at this wrong, but I think you made one error in your calculation on the taxes payable for the $900 investment. Since the $900 is an after tax investment, it would not be taxed again when it is removed. Asuuming the investment was made in some kind of tax deferred vehicle, you would be taxed on gains of $712. After taxes at 15%, you would be left with $605 plus the original $900, for a total amount of $1,505. When added to the traditional IRA distribution (after tax) of $9,133, you have a total net value of $10,638. This is still $107 less than the net value of the Roth IRA. The result would be different if the $900 was in vested in a taxable account and the gains were taxed every year, but that calculation is a little more than my tired brain can puzzle through at the moment.