I think you are confusing expected returns on capital with retirement portfolio income. You can't generate income of 10% on a simple equity portfolio (unless you have a steady source of insider color or something).Why go through the headache of trading if I can get ~10% just holding RUT long term?
In case of this guy, he'd want to take out X dollars out of his retirement egg. People here are suggesting that he can lead a lifestyle that's equal to 15% of his holdings. I think that's very aggressive and will blow him up fairly quick.
Honestly, I think realistic number for an average person is 4 to 5% draw on his inception capital and for a trader that's very good it's probably 6 to 8. There are many other parameters to this, such as age, health, other investments etc.