From the F.E. site:
"To estimate your retirement income, we use a process called annuitization and adjust for inflation to translate estimated portfolio values at retirement age into annual pre-tax estimated retirement incomes in today's dollars."
In other words (as I understand it), they assume you will convert your portfolio at retirement to an annuity and have that income stream along with any others (SS, pension, etc.) There is no assumption that you have to "plan" while you are retired.
That makes little sense since one of the "strongly suggested" facts concerning an annuity (more specifically an SPIA) is not to annuitize more than 50% of your portfolio.
F.E.'s said that they were working on a "retirement version" for at least the last five years (when I started questioning them). Of course, I don't pay for the service (I get it free via VG) so I really don't care.
For my heavy lifting, I use Fidelity's RIP (and cross-checked with other products, such as FIRECalc).