Read a little further. He has a special needs kid. I don't know how demanding that is for him but I do know that getting the worklife/homelife balance right and finding time to exercise can be quite a challenge even with regular kids.

And btw, I've read his blog for some time now. While I don't make all the same personal choices as he does when it comes to getting things done, I've found his reasoning-from-principles approach to it very helpful.